Thanks auxsvr for your reply. I will check that and report the result here in this thread.

Today it happened thrice. I had three freezes while working. No set pattern of the problem. One common factor is during all these crashes I was in Firefox, I don't think that can be any problem. Still I mentioned here because may be any information can be crucial in solving a problem.

Edited
------
Checked. It's 64MB in BIOS settings. Although I do not understand much about these settings but actually there is only one Video RAM setting option. So I think I checked it correctly.

Should I go for another fresh install. It's painful to again set up everything from scratch.

Reinstalling is not necessary in general, the video driver must be at fault. You can try disabling AIGLX by adding in the serverlayout section of the /etc/X11/xorg.conf file. I'm afraid I cannot help you any more than this. If hangs still insist, you should file a bug report in novell bugzilla.

Ok, I will follow the guidelines. I will inform later about the developments. Thanks again for so much help.

No, adding that option also didn't solved the problem. System freezes again.

I had similar problems, ran memtest which seemed to suggest the memory was ok, but after a few days of crashes ran memtest again, but this time kept it going overnight. When I looked at it in the morning, there were errors.

I would say with certainty that it is your memory at fault. Run memtest for 24 hours, that should prove it.

Thanks for your suggestion. I will run that at next available opportunity (may be the next weekend). As this stick is a brand new stick, I will have to then ask for replacement from the Dealer if the stick is at fault.

Why don't you try simply to take out the new RAM-stick.
If your system becomes stable - although slower - You've found the error.

Just an idea.

Yes that is what I am going to do if the problem happens again. As of now the system seems stable and working for long hours. Yesterday I could not work, so today I will understand what next I have to do.

Thanks jan-portugal for the suggestions.