Major Computer problem.

I am a newbie here and have some major problems with my computer.Here is howthe story goes..

I have an old Athlon 900 Mhz computer with a K7S5A motherboard (It is the very early models. It does not have revision no. on it).
It had been working fine till now. I installed a new HD and had to reinstall all my software. Everything looked fine till I installed Nero (the latest revision from their website). It gave me a message that this has a known compatability issue with Windows XP and to go and install a patch. I could not find the patch in their website. Anyway, anytime I would try to burn a CD, the computer would reboot and it would reboot again when loading XP. This would go on till I would take the CD out of the drive. Then it would reboot and work normally.

I unistalled the latest version of Nero and installed the older version that I had and it is still rebooting.

I ran this eventvwr application and it found the following error:

"The device, \Device\CdRom0, has a bad block.

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp."

I went to the microsoft website to find it but could not find anything pertinent.
I have now updated my Nero with the patch and updated my CR writer's firmware. I burned one CD without any hitch but when I tried to do a multisession burn on the same CD, the computer turned itself off immediately. I have to clear the CMOS inorder for it to start up without shutting down immediately. I really don't know what is going on...

Can someone advise me what to do at this point to remedy the problem?