xp goes black on start up

1.7 gig p4 512mb ddr 30gb ata 133 win. xp pro

when i turn it on, it will turn on normal and go to the xp splash screen but it will take longer then expected and the go to black and nothing happens. so i decieded to repair it with the xp disk. now it goes through half the repair gives me an error with lass and then i click ok and it restarts the computer.

thank u for ur help