Graphics card or North bridge?

Thus, the system
The CPU type QuadCore Intel Xeon E5440, 2833 MHz (8.5 x 333)
Motherboard ASRock G41M-VS3 (1 PCI, 1 PCI-E x16, 2 DDR3 DIMM, Audio, Video, LAN)
The video card GeForce GT 640 (1 GB)
RAM of 2 laths on 4 GB Crucial CT51264BD160B.C16F DDR3-1600 DDR3 SDRAM
Disk drive HGST HTS545050B7E660 ATA Device (500 GB, 5400 RPM, SATA-III)
(I can throw more information)

So I bought this card with avito in September (previous complete set was even worse) after three months started to catch artifacts (replaced the thermal paste, software and increased the speed of the cooler, the average temperature of the video card 30 - 45 degrees), the artifacts still continued to come out, but less (as you get to play and I've been a little lazy on them). But after the new year the problem has intensified after the appearances of the blue screen. Now the artifacts climbs even after 30 minutes of watching VIDOS on YouTube, at least 3 hours when playing in the subway. I thought that the problem in the video card, there is no money to replace it so was trying to find an alternative solution to the problem. And suddenly decided to check the North bridge, it was very hot (in Hades could not see because of the missing sensors) is 70-80 degrees.
Experts, help!