Windows keeps re-starting, cannot boot from xp cd

Hello,

When I start my computer, it reaches upto the windows xp image with the blue bar below below it, but then it immediately restarts the computer.

I tried booting the computer with windows xp cd. During the boot time the computer reads from the cd but some how bypasses the bios settings and starts booting from the harddisk again. And then the computer again restarts.

I have tried different startup cds. Nothing works.

I believe its got something to do with a virus or something. Pls help urgently.

Thanks a lot.
Kris.