Operating System not starting

My brother built a computer from the bottom up and it worked fine for a while. One day however, he went to turn it on and it came to the motherboard start-up screen and then the screen went black. He thinks that somehow the operating system got whipped out or the harddrive is fried. Any ideas as to what it might be and how we could fix it? Any response would be appreciated, Thanks

 

Hmmm... very vague question, a bit light on details. First, have you tried safe mode? You say you get the motherboard screen (also called the "post") and then it goes black. In the top left corner, is there a blinking cursor? Visit the hard drive maker's web site. Download and run their diagnostic tool. They'll have one (it's free) that will create a bootable CD or floppy disk. You boot to it on the 'crashing' PC, and it will test the hard drive, and many times it will repair it. Does the PC restart over and over? Or it just goes to a black screen with nothing? Are there any strange sounds like a grinding or clicking sound? Are there any blinking lights on the PC? What brand is the motherboard? What brand is the hard drive? What about the BIOS? Have you checked the boot order? Is the BIOS recognizing all the devices like the hard drive and CD drives? Have you tried to boot to the CD/DVD drive? More info please!!!

...and Welcome to MajorGeeks! :major