Gtx 680 superclocked

I had graphic card problem ( it's fan was going crazy + screen wouldn't show up. )
im writing this with onboard graphic card. what seems to be the problem???
Fan was going really fast and making really loud sound. and screen went black.
and


second question is , after the problem, i pulled out the GPU and putted it again and i don't know what i did wrong. i simply connected the gpu on motherboard,( i didnt connect power) and started computer , and graphic card cut on smoke. i dunno why.
what wouldbe the problem