Lol!
Overheating seems like a reasonable explanation, gonna try prime95 now
Spec:
Amd Penom(tm) II X4 b55 (4CPUs) ~ 3.2GHz
4096MB RAM (DDR3)
AND Radeon HD5750
With GPU mining on Radeon HD5750 you could get much more than 7 kHs/s - up to 180-190 kHs/s max.
Try cgminer or bfgminer.