Windows XP boot problem

3 year old Dell 4600 has developed a boot problem. Just prior to the problem I was deleting some large avi files to regain disk space. With each deletion the screen would black out for a second, then return. Finally it went black, froze, and I had to shut the machine off to reboot. Since then, on boot up I see the usual RAM check, the usual text scrolling by, the Win XP splash screen and progress bar, then it goes black and stays that way instead of bringing up the login screen. After a couple of minutes, the hard drive clicks off and spins down. But, after restarting I can press F8 and boot to Safe Mode without a problem. What I have tried that hasn't helped: boot to last good configuration, loading a system restore point several times, checking the C drive for errors.