Ok, my brothers Dell latitude E6400 laptop stopped working, he was just browsing the internet, and everything froze. he held down the power button and it shut off. now whenever he tries to boot, it gets to the windows loggin screen, and after he puts in his password, it says welcome, and after 20-30 seconds, the screen goes black. he has tried running in safe mode, he cleaned it all out, tried running with and without the battery, but nothing is working. anyone here have an idea whats wrong? btw he has windows 7 64-bit.