Help with partition / OS

Computer is custom built, 2 years old, Has amd Phenom 2 ,4 core processor, asrock mother board, 8 gigs ram, windows 7 pro. Four days ago the system would not boot, I tried to repair it with my win 7 cd, it could not recognize a partition or OS, could not repair, I had another hard drive handy, I installed it, loaded win 7, fixed! Three days later, I have the same same dilemma,I would like to fix myself, it seems that it may be more than hard drive failure, maybe a bad mother board?, Virus? Any help would be appreciated.