broken windows xp

I got a windows xp home computer, jsut the other day I got it working fine after removing several viruses, now when I turn on the computer everything goes fine until it gets to the splash screen where it shows windows xp loading, and the loading bar is moving. Except the OS never shows up, in fact it will reboot on me then come with the safe mode screen like i pulled the power. What is wrong with my computer and how do I fix please?