Printer HP Officejet Pro 8500 is not recognized after sucessfull installation of HPLIP

I followed the installation procedure described here:
http://axebase.net/blog/2014/12/05/installation-hp-linux-imaging-and-printing/#comment-3367

However, I have the following problem: "hp-setup -i" gives me

HP Linux Imaging and Printing System (ver. 3.16.7)
Printer/Fax Setup Utility ver. 9.0

Copyright (c) 2001-15 HP Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

(Note: Defaults for each question are maked with a ‘*’. Press to accept the default.)

——————————–
| SELECT CONNECTION (I/O) TYPE |
——————————–

Num Connection Description
Type
——– ———- ———————————————————-
0* usb Universal Serial Bus (USB)
1 net Network/Ethernet/Wireless (direct connection or JetDirect)

Enter number 0…1 for connection type (q=quit, enter=usb*) ? 1

Using connection type: net

error: No device selected/pecified or that supports this functionality.

Note: Pressing 0 or enter leads to the same error.
The printer is connected to the power and connected via usb to the computer. I restarted the computer as asked. I restarted the printer. I replugged the printer. In all possible combinations.
My printer type: HP Officejet Pro 8500 (HP Officejet Pro 8500 Wireless All-in-one Printer – a909g).
My System: Linux-Mint-Version 17.2, 64bit

I have another printer installed, but not working (Brother). When I run hp-doctor, I get the following result:

HP Linux Imaging and Printing System (ver. 3.16.7)
Self Diagnse Utility and Healing Utility ver. 1.0

Copyright (c) 2001-15 HP Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

HP Linux Imaging and Printing System (ver. 3.16.7)
Self Diagnse Utility and Healing Utility ver. 1.0

Copyright (c) 2001-15 HP Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

Checking for Deprecated items....
No Deprecated items are found

Checking for HPLIP updates....

HP Linux Imaging and Printing System (ver. 3.16.7)
HPLIP upgrade latest version ver. 1.0

Copyright (c) 2001-15 HP Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

Latest version of HPLIP is already installed.

Checking for Dependencies....

---------------
| SYSTEM INFO |
---------------

 Kernel: 3.16.0-38-generic #52~14.04.1-Ubuntu SMP Fri May 8 09:43:57 UTC 2015 GNU/Linux
 Host: GrossesMonster
 Proc: 3.16.0-38-generic #52~14.04.1-Ubuntu SMP Fri May 8 09:43:57 UTC 2015 GNU/Linux
 Distribution: 22 17.2
 Bitness: 64 bit

-----------------------
| HPLIP CONFIGURATION |
-----------------------

HPLIP-Version: HPLIP 3.16.7
HPLIP-Home: /usr/share/hplip
HPLIP-Installation: Auto installation is supported for linuxmint distro 17.2 version

Current contents of '/etc/hp/hplip.conf' file:
# hplip.conf. Generated from hplip.conf.in by configure.

[hplip]
version=3.16.7

[dirs]
home=/usr/share/hplip
run=/var/run
ppd=/usr/share/ppd/HP
ppdbase=/usr/share/ppd
doc=/usr/share/doc/hplip-3.16.7
html=/usr/share/doc/hplip-3.16.7
icon=/usr/share/applications
cupsbackend=/usr/lib/cups/backend
cupsfilter=/usr/lib/cups/filter
drv=/usr/share/cups/drv/hp
bin=/usr/bin
apparmor=/etc/apparmor.d
# Following values are determined at configure time and cannot be changed.
[configure]
network-build=yes
libusb01-build=no
pp-build=no
gui-build=yes
scanner-build=yes
fax-build=yes
dbus-build=yes
cups11-build=no
doc-build=yes
shadow-build=no
hpijs-install=no
foomatic-drv-install=no
foomatic-ppd-install=no
foomatic-rip-hplip-install=no
hpcups-install=yes
cups-drv-install=yes
cups-ppd-install=no
internal-tag=3.16.7
restricted-build=no
ui-toolkit=qt4
qt3=no
qt4=yes
qt5=no
policy-kit=no
lite-build=no
udev_sysfs_rules=no
hpcups-only-build=no
hpijs-only-build=no
apparmor_build=no

Current contents of '/var/lib/hp/hplip.state' file:
Plugins are not installed. Could not access file: Datei oder Verzeichnis nicht gefunden

Current contents of '~/.hplip/hplip.conf' file:
[upgrade]
notify_upgrade = false
last_upgraded_time = 1470086010
pending_upgrade_time = 0
latest_available_version = 3.16.5

[installation]
date_time = 01.08.2016 21:59:08
version = 3.16.7

 <Package-name> <Package-Desc> <Required/Optional> <Min-Version> <Installed-Version> <Status> <Comment>

--------------
| COMPILEDEP |
--------------

 gcc gcc - GNU Project C and C++ Compiler REQUIRED - 4.8.4 OK -
 make make - GNU make utility to maintain groups of programs REQUIRED 3.0 3.81 OK -
 libtool libtool - Library building support services REQUIRED - 2.4.2 OK -

------------------------
| General Dependencies |
------------------------

 libcrypto libcrypto - OpenSSL cryptographic library REQUIRED - 1.0.1 OK -
 python-xml Python XML libraries REQUIRED - 2.1.0 OK -
 libnetsnmp-devel libnetsnmp-devel - SNMP networking library development files REQUIRED 5.0.9 5.7.2 OK -
 sane-devel SANE - Scanning library development files REQUIRED - 1.0.23 OK -
 pil PIL - Python Imaging Library (required for commandline scanning with hp-scan) OPTIONAL - 1.1.7 OK -
 pyqt4-dbus PyQt 4 DBus - DBus Support for PyQt4 REQUIRED 4.0 4.10.4 OK -
 libpthread libpthread - POSIX threads library REQUIRED - 2.19 OK -
 python-devel Python devel - Python development files REQUIRED 2.2 2.7.6 OK -
 cups-devel CUPS devel- Common Unix Printing System development files REQUIRED - 1.7.2 OK -
 python-dbus Python DBus - Python bindings for DBus REQUIRED 0.80.0 1.2.0 OK -
 cups-ddk CUPS DDK - CUPS driver development kit OPTIONAL - - OK -
 reportlab Reportlab - PDF library for Python OPTIONAL 2.0 3.0 OK -
 pyqt4 PyQt 4- Qt interface for Python (for Qt version 4.x) REQUIRED 4.0 4.10.4 OK -
 libusb libusb - USB library REQUIRED - 1.0 OK -
 cups-image CUPS image - CUPS image development files REQUIRED - 1.7.2 OK -
 python2X Python 2.2 or greater - Python programming language REQUIRED 2.2 2.7.6 OK -
 python-notify Python libnotify - Python bindings for the libnotify Desktop notifications OPTIONAL - - OK -
 libjpeg libjpeg - JPEG library REQUIRED - - OK -
 sane SANE - Scanning library REQUIRED - 1.0.23 OK -

----------------------
| Scan Configuration |
----------------------

 scanext Scan-SANE-Extension REQUIRED - 3.16.7 OK -
 hpaio HPLIP-SANE-Backend REQUIRED - 3.16.7 OK 'hpaio found in /etc/sane.d/dll.conf'

-------------------------
| External Dependencies |
-------------------------

 gs GhostScript - PostScript and PDF language interpreter and previewer REQUIRED 7.05 9.10 OK -
 cups CUPS - Common Unix Printing System REQUIRED 1.1 1.7.2 OK 'CUPS Scheduler is running'
 network network -wget OPTIONAL - 1.15 OK -
 scanimage scanimage - Shell scanning program OPTIONAL 1.0 1.0.23 OK -
 policykit PolicyKit - Administrative policy framework OPTIONAL - 0.105 OK -
 xsane xsane - Graphical scanner frontend for SANE OPTIONAL 0.9 0.998 OK -
 dbus DBus - Message bus system REQUIRED - 1.6.18 OK -
 avahi-utils avahi-utils OPTIONAL - 0.6.31 OK -

---------------------
| Python Extentions |
---------------------

 hpmudext IO-Extension REQUIRED - 3.16.7 OK -
 cupsext CUPS-Extension REQUIRED - 3.16.7 OK -

------------------------------
| DISCOVERED SCANNER DEVICES |
------------------------------

No Scanner found.

--------------------------
| DISCOVERED USB DEVICES |
--------------------------

No devices found.

---------------------------------
| INSTALLED CUPS PRINTER QUEUES |
---------------------------------

Brother-DCP-115C
----------------
Type: Unknown
Device URI: usb://Brother/DCP-115C?serial=BROH6F950894
PPD: /etc/cups/ppd/Brother-DCP-115C.ppd
PPD Description: Brother DCP-1200 Foomatic/hl1250 (recommended)
Printer status: printer Brother-DCP-115C disabled since Mo 01 Aug 2016 21:20:20 CET - Unplugged or turned off
warning: Printer is not HPLIP installed. Printers must use the hp: or hpfax: CUPS backend for HP-Devices.

--------------
| PERMISSION |
--------------

Checking Permissions....

Checking for Configured Queues....
warning: Device Brother-DCP-115C is not HPLIP installed. Device must use the hp: or hpfax: to function in HPLIP.
warning: Brother-DCP-115C is not HP Device.

warning: No Queue(s) configured.

Checking for HP Properitery Plugin's....
No plug-in printers are configured.

Diagnose completed...

More information on Troubleshooting,How-To's and Support is available on http://hplipopensource.com/hplip-web/index.html

Any kind of help would be greatly appreciated!