XP Pro OS Quick Freeze

I just purchased a brand new system about a week ago off the internet (STUPID,I know!). Yesterday it started to freeze after about a minute or so. And I mean FREEZE! No mouse, keyboard, the clock stops and Ctrl-Alt-Del doesn’t even work. It freezes in any situation on any screen after about a minute or sometimes a few minutes. I just tried booting off of the CD, and it seems to work that way.

Any ideas? Thanks!