Storage

Hey. I just bought a pc for my little brother. His system would not boot up on a barebones test, but everything seemed to work but the fan on his videocard which did not start up, and we got nothing on the screen. So we tried my gtx 770 and sure enough, I got a picture. Then we tried his card in my pc, and that worked. So do anyone know any possible reasons to his card not working in his pc when every other combination of cards and the rest with my pc work?

His specs:
1 Cooler Master Elite 430 (USB 3.0) Black

1 Cooler Master B500v2, 85% efficiency, 500W PSU

1 AMD AM3 FX-6300, 95W

1 ASUS AM3 M5A97 R2.0

1 Crucial DDR3 BallistiX 1600Mhz 4GB KIT

1 Sapphire Radeon R7 240 2GB

1 Seagate Barracuda® 1TB SATA3.0

1 ASUS DVD Writer, DRW-24F1ST, SATA, Black, Retail

1 Crucial DDR3 BallistiX Sport 1600MHz 4GB

My specs (2 yrs old)(dont have them perfectly, but they dont really matter that much becasue mine works?)

Gtx 770
Msi motherboard
8GB of ram
intel 4770 processor
I think a 600w PSU