Ubuntu 16.04 LTS random crashes, mouse works

Have you tested your RAM using Memtest86 from GRUB?

Sadly my Grub (202b2) does not offer the Memtest86 option anymore.
Is there a way to start it in terminal?

It's under the advanced options.

Sadly not in my version of GRUB.

What is output of:

lsb_release -a; dpkg -l | grep -i mem

Thanks

richard@richard-Predator-G3120:~$ lsb_release -a; dpkg -l | grep -i mem
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04.3 LTS
Release: 16.04
Codename: xenial
ii libasan2:amd64 5.4.0-6ubuntu1~16.04.5 amd64 AddressSanitizer -- a fast memory error detector
ii libitm1:amd64 5.4.0-6ubuntu1~16.04.5 amd64 GNU Transactional Memory Library
ii liblsan0:amd64 5.4.0-6ubuntu1~16.04.5 amd64 LeakSanitizer -- a memory leak detector (runtime)
ii libmpx0:amd64 5.4.0-6ubuntu1~16.04.5 amd64 Intel memory protection extensions (runtime)
ii libtalloc2:amd64 2.1.5-2 amd64 hierarchical pool based memory allocator
ii libxshmfence1:amd64 1.2-1 amd64 X shared memory fences - shared library
ii libxshmfence1:i386 1.2-1 i386 X shared memory fences - shared library
ii memtest86+ 5.01-3ubuntu2 amd64 thorough real-mode memory tester
ii python-talloc 2.1.5-2 amd64 hierarchical pool based memory allocator - Python bindings
richard@richard-Predator-G3120:~$

It's installed. What is the output of:

sudo update-grub

richard@richard-Predator-G3120:~$ sudo update-grub
[sudo] password for richard:
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-4.4.0-104-generic
Found initrd image: /boot/initrd.img-4.4.0-104-generic
Found linux image: /boot/vmlinuz-4.4.0-103-generic
Found initrd image: /boot/initrd.img-4.4.0-103-generic
Found linux image: /boot/vmlinuz-4.4.0-101-generic
Found initrd image: /boot/initrd.img-4.4.0-101-generic
Found linux image: /boot/vmlinuz-4.4.0-98-generic
Found initrd image: /boot/initrd.img-4.4.0-98-generic
Found linux image: /boot/vmlinuz-4.4.0-97-generic
Found initrd image: /boot/initrd.img-4.4.0-97-generic
Found linux image: /boot/vmlinuz-3.13.0-37-generic
Found initrd image: /boot/initrd.img-3.13.0-37-generic
Found linux image: /boot/vmlinuz-3.13.0-36-generic
Found initrd image: /boot/initrd.img-3.13.0-36-generic
Found linux image: /boot/vmlinuz-3.13.0-24-generic
Found initrd image: /boot/initrd.img-3.13.0-24-generic
Found Windows Recovery Environment (loader) on /dev/sda1
Found Windows 7 (loader) on /dev/sda2
Found Windows 7 (loader) on /dev/sda3
done
richard@richard-Predator-G3120:~$ lsb_release -a; dpkg -l | grep -i mem
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04.3 LTS
Release: 16.04
Codename: xenial
ii libasan2:amd64 5.4.0-6ubuntu1~16.04.5 amd64 AddressSanitizer -- a fast memory error detector
ii libitm1:amd64 5.4.0-6ubuntu1~16.04.5 amd64 GNU Transactional Memory Library
ii liblsan0:amd64 5.4.0-6ubuntu1~16.04.5 amd64 LeakSanitizer -- a memory leak detector (runtime)
ii libmpx0:amd64 5.4.0-6ubuntu1~16.04.5 amd64 Intel memory protection extensions (runtime)
ii libtalloc2:amd64 2.1.5-2 amd64 hierarchical pool based memory allocator
ii libxshmfence1:amd64 1.2-1 amd64 X shared memory fences - shared library
ii libxshmfence1:i386 1.2-1 i386 X shared memory fences - shared library
ii memtest86+ 5.01-3ubuntu2 amd64 thorough real-mode memory tester
ii python-talloc 2.1.5-2 amd64 hierarchical pool based memory allocator - Python bindings
richard@richard-Predator-G3120:~$

Hmm, seems to not be added to grub. The install CD should have this feature too. If the system is crashing then checking the RAM where the applications reside while they run is a good first step.

The Ultimate Boot CD also has this but Memtest86 also has an ISO you can transfer the ISO to a USB stick or CD and boot to that.