At boot up , the PC gets to the point of loading Windows XP then shuts itself off and restarts . Any advice ? Thank you ...

do you get any beeps, can you boot into safe mode?

Thanks for responding brain damage ...

The problem just started yesterday . Never get to see the clock - it never gets to the desktop . Windows XP starts to load - the progress bar below starts , after a moment the screen goes blank and then the computer restarts . HP computer : we did just get X-box live and bought a router and installed that the other day , but it was working fine for a day or so after that .

Try booting into Safe Mode by repeatedly tapping the F8 key after your BIOS POST but before Windows starts.

Choose Safe Mode / System Restore.