Crysis Artifacts

Need help.

I recently bought a Noctua NH-U9B SE2 for my E6550 and I can push it to 3.465 Ghz top.
Other hardware are remain the same.
My spec:
E6550 - Asus P5KC - Kingston 2x1Gb DDR3 PC10600 value RAM, 320 Gb Seagate 32 Mb chace, HIS HD4830 IceQ 512 Mb 256 bit DDR3.

Since my case doesn't have back hole to attached the back plate cooler, I remove the mobo from the case and also unplug the GPU. After finished, put back together, and start OC.

When I tried to play Crysis, some lines appears randomly like long distance, or vertically.
Also there are noticeable area where the ground or valley in crysis appears like rough boxes.
It that artifacts?

I've played Crysis before with proc stock speed, oc to 2.8Ghz, GPU stock speed, GPU OC (core @575Mhz memory @1090Mhz) and I never had a problem like this.
What happen to my PC??? I also tried to play with both Proc and GPU stock speed, the artifacts reduced, but sometimes it showed up.

I then unplug and plug in the GPU again but this still happen.