hp pavilion 752n not working worked yusterday now it doesent

i have a hp pavilion 752n with a 2.0 GHz pentium 4 processer 512mb of ram it worked yusterday now it doesent work. i reinstalled windows on the hard drive and when it goes to start it says windows shut down unexpectedly start windows normaly start in safe mode or last known good configuration. if you click eather start windows normaly or last known good configuration it goes to the windows loading screen and when it goes to go to the welcome screen i get a blue screen wity white letters and numbers but it goes by to fast and i cant read what it says and the computer powers down then back up and it continiously does this i have know idea why it isent working any help would be greatly apreashiated