Can someone tell me why my ubuntu 12.04 freezes often?

Have youbtried the 2D session which is selectable from the login screen?

Nobody has given you a proper solution as you have never asked for a solution. How can we know you are having an issue if this is the first time we have heard about it?

Yes I've tried 2D session. Ubuntu freezes on 2D session too.

Hello andrew,

"Nobody has given you a proper solution as you have never asked for a solution. How can we know you are having an issue if this is the first time we have heard about it?"

I already reported this bug here and asked for help one month ago.

I couldn't get proper solution. I'm googling everyday to get a proper solution.

https://answers.launchpad.net/ubuntu/+question/243716

Have you tested your RAM using Memtest86 from Grub?

Yes I tested my RAM using memtest86. It said "test passed.. No errors"

First: disable ACPI as explained here:

http://askubuntu.com/questions/300147/how-can-i-troubleshoot-why-ubuntu-keeps-crashing-on-my-laptop

Then run

watch -n1 "ps aux > ~/Desktop/ps.txt"

in tty1 as explained here:

http://ubuntuforums.org/showthread.php?t=2191480

Inspect the contents of the file ~/Desktop/ps.txt after the next freeze to see which process is causing the crash.

If the PC still crashes and you cannot find the origin of the crash, I suggest testing Ubuntu 13.10.

Then disable ACPI and run the watch command again in Ubuntu 13.10.

If it still crashes in Ubuntu 13.10, update the BIOS using this procedure:

Go here

http://www.acer.co.uk/ac/en/GB/content/drivers

Search for your laptop via the following serial number:

NXRTHSI00121201B796600

Click on BIOS.

Click on "All" to switch from "latest" to "all".

Download and flash BIOS version 2.19 (to upgrade from V2.17 to V2.19):

BIOS Acer BIOS 2.19 8.0 MB 2012/04/30 Download

Then retest Ubuntu 13.10 with ACPI enabled and also with ACPI disabled.

Hope this helps....

Thanks Mark..
I'll try your suggestions

Hello Mark. Your suggestion works fine.

I edited this file

sudo gedit /etc/default/grub

abd changed this line

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi=Linux acpi_backlight=vendor"

to this line

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi=off"

Now my ubuntu working fine without any freeze.

However some of my display functions not working. My battery status icon disappeared, my shutdown function not working properly, My brightness control not working correctly and so on

Is there a way icon fix this problems without enabling acpi?

Try experimenting with the acpi /etc/default/grub settings as explained in the section "Common Kernel Options" in the following link:

https://help.ubuntu.com/community/BootOptions

You will need to try each option one by one (reboot each time) until you find the best option.....