sounds to me like either faulty ram or mother board... try taking all but one stick of ram out, then switch them out every time it doesn't work untill you have tested each stick. If that works, then it was just ram... if not i'm afraid it's probably more serious. First though, try to put your OS disk in and reformat and see if that will correct the problem, then if not get into your bios (if you can) and try to see if it is recognizing your hard drive. If none of that works then you probably have a bad motherboard.