XP will not boot up

My desktop will not boot to Windows. I turn the pc on, the memory is tested "ok ", then it goes to this page that says " we appologize for the inconvenience, but windos did not start successfully. a recent hardware or software change might have caused this ".........goes on then gives the options to either start in safe mode, safe mode with networking, safe mode with command propmt, last known good configuration, or start windows normally. I have chosen everyone of them only to find the same result: after I choose one of the options, it goes to the "windows xp home edition" screen with the little sliding green bar underneath, this screen stays up for about 20 or so seconds, then the pc just restarts and does the whole thing over again. I haven't installed any software or hardware lately, so I can't figure out why the pc would just all of a sudden start acting like this. Any ideas?

 

An easy and harmless thing you can do that may well fix things is to use the install CD and boot to the Recovery Console.

Once there type in
chkdsk /r and ENTER to run it.

If that doesn't fix things, back to the recovery console and fixboot.

If still no joy, try removing all possible bits of hardware and trying to boot up. If you can lay hands on a different video card, I'd also try with that rather than your present one.