Locking up on boot

[FynexFox]

Hey everyone, hows it going? I got a problem where my computer locks up while Windows is loading. the computer is pretty much a stock HP - all I added was a ati radeon 9600gt, changed PSU, and added 512mb of ram. This computer wored fine with everything it has now - before - the PSU is different from what was in it in its working condition though. heres what happens - when I start up it gets the the screen with the windows logo and scrolling bar, the abr scrolls a few tiems thens tops, same aplce every time, Ive tried it with XP home 3 times and xp pro 2 times, stops in the same place every time, which confused me. works in safe mode though...