abrupt shutdown during bitcoin mining

[tarui]

my system specs
amd 6990. 880/1250 stock volts/
aircooling.
amd 11.6 drivers

for some reason it seems to have some sort of a partial crash during mining after a few minutes, anything from 3mins to 15+mins. it's not like I tried to play a video file or anything that directly triggered the crash.

what happens is that, the screen goes blank, gpu fan spins at idle instead of load speed, the motherboard's debug led shows AO (normal)

using msi afterburner's monitoring software, i noticed when it crashes,the gpu temp falls from 80+  to -1 on both GPUs.
fan speeds jump from 98% to 200%
gpu usage jump from 98% to 200%
gpu rpm jump from 3000+ rpm to 3889967360.000
core clocks frm 880 to 13.578 on both gpus.

or did mining/i somehow killed the gpu?

[macintosh]

The mining must be eating all your CPU power away