Alienware X51 R2 crash due to GPU

So I bought this PC back to August, 2014. It works fine till the last month. One day, I was playing like normal then suddenly the screen turn black and show the message "No HDMI Cable". I shut it down and turned it back again using the other HDMI port of intel graphic, it worked fine so I concluded that the Graphic card cause this problem. The day after, I turned my Pc on using GPU HDMI port and it worked for a few days, then it started freezing and I had to reset the Pc. Till now I've tried many drivers for the GPU but It cannot fix the problem, it keeps freezing even when I browsing internet then I have to restart again with the intel graphic. The fan works fine, the temparature is not too hot (60~75 when gaming) cuz I use the Msiafterburner to raise the fan speed, I haven't OC.  This really annoys me and I'm starting scare to play game or even browsing with this GPU. Any help pls ?