how do I fix a hard drive?

My daughter turned her computer on last weekend, only to find out that it says there isn’t any hard drive, only the cd rom and floppy drive. She doesn’t have internet access on that computer so it probably isn’t a virus. I went in and made sure that all the connections were secure. I even went to the point that I changed the cable going to the motherboard, without any result. What could have caused it, and is there any way to restore it?