That doesn't tell us too much...plus I wouldn't trust Geek Squad at all after seeing some of their shotty repairs.
3 things to check. Visually inspect the motherboard and find if there are any bad capacitors. How to tell? They should be flat on top. Any slight bulge or leakage a sign it's bad. If it all looks good, test the RAM. A program like Memtest86 is probably best; just let it run overnight. If you don't get any errors, scan the hard drive. Either find a program made specifically for that drive (from the manufacture) or Seatools works for most makes/models of drives (you might need to disable AHCI)
If you're unable to boot to a CD and run any of these test, and you're 100% sure you had the boot order and all set right, then your board is probably bad.