Windows XP won't boot

My desktop at home runs Windows XP home and it's been doing fine for as long as I've had it. I just ran a disk cleanup and a defragmentation a few days ago and it seemed fine. The next day however, the computer was acting strange. It boots to the screen where you can select to start Windows normally or in Safe mode and I have tried all the options on that page to no avail.

When I start it normally it goes to the Windows XP loading screen as usual, but after a few seconds, it beeps, the screen goes black and the computer restarts itself. With all the options it just ends up restarting with never getting to Windows.

I've looked all over the internet and it seems the only option is to boot from a Windows XP cd, but I don't have one since the desktop was given to me by a friend when I moved and they got a new computer.

Anyone know how to fix this?

Will it not boot into safe mode? If it does, goto the system properties

Start->Control Panel->System (or WinFlag key+Pause|Break) Advanced and turn off the automatic reboot and this will show the stop code on the BSOD. that code will tell you what's failing.
Good luck

Have a quick peek inside the case and make sure all your motherboard's capacitors are ok. (Not bulging or leaking).

if you can lend a xp disc you could boot from it and start the recovery console and type fixboot to see if that resolves it