Go to your BIOS and see if anything is out of the ordinary, like your PC not booting without a keyboard or something, also check inside, maybe you pulled a power plug inside, make sure everything is connected to either a four pin large or a four pin small
A few days ago while I was using my computer (compaq presario R4500) it locked up so I had to manually restart it by pressing the power button. Now it won't boot up. I turn it on and it goes as far as the windows xp splash screen and then the screens flicks and it restarts. I tried safe mode and started from the last time it worked options and the same thing happened. Anyone have any tips??