hi,
a few weeks ago i installed Ubuntu 9.10 on my PC on which i was previously using Ubuntu 8.10. However after the installation of the new version, my machine keeps hanging all the time,like i can use it for 20 minutes and it hangs and completely freezes, so i have to force a shutdown in order to restart and it does so very often, i don't know where the problem really is. The PC is Pentium 4, 40GB hard disk, 512MB RAM, processor speed of 1.8 GHz, i am really fed up with this problem, please assist me if you can, and let me know if you need more details,

Thanks in advance

Graphics card?

Have you tried the current Ubuntu release (10.10)? 9.10 is over a year old and only has a few months of support left...

i hope you will be able to know the type of graphics card being used from the information below which i got from the terminal,

VGA compatible controller: Intel Corporation 82915G/GV/910GL Integrated Graphics Controller (rev 0e)

I never had good luck with my Intel graphics card on Ubuntu 9.10. If you refuse to update to the current version for some reason, a quick fix you can try is to disable Compiz desktop effects.

i'll try and update them and see whether it makes a difference, then i'll get back to you

You don't need to update anything yet; just burn an Ubuntu 10.10 Live CD and take it for a test drive. If it solves your "crashes every 20 minutes" problem, then you know the problem is specific to 9.10 and you can either upgrade or do a fresh reinstall of 10.10 (my recommendation).

Also, did you try my "disable compiz effects" suggestion? It is potentially a 5-second, no-risk solution to your problem.

i think i'll simply try out ubuntu 10.1 and see how things go, i haven't tried 'disable compiz effects' because i don't know how to go about it, i typed it in the terminal and it replied that command 'disable' was not found.

There is no 'disable' in the command I suggested:

You can also go to System-Preferences-Desktop Effects, or right-click on the background, choose Appearance, then Desktop Effects.