Help! HD 7970 not detected in PCIe 1, and post error in PCI 2

My HIS HD7970 worked fine for about two years untill it stopped being detected in the first PCIe slot, I tried reinstalling drivers (useing the onboard graphics) and it worked for awhile untill it happened again, so I put it in the second PCI slot and it worked fine for a year and a bit untill one day it won't complete post showing error 62 (INSTALLATION OF SOUTH BRIDGE RUNTIME SERVICES), now I'm useing a GTX 480 and it works in both PCI slots so it's not the slots, what could be the problem?

Help! HD 7970 not detected in PCIe 1, and post error in PCI 2