Troubleshooting GPU issue on my laptop

Hi,

I would like to fix my Dell Vostro 3700 that haven't used for a few months. The GPU seems to be dead. When I use the laptop, after about 10 minutes I start seeing strange colored squares for a few seconds, or a black with a few colored lines, then sometimes it gets back to normal with a message in the toolbar (sorry I forgot what this message says but it's something like "the graphics have been recovered"), and other times it just freezes or reboot. Before this behaviour started to occur, I had overheating issues, which made me buy a desktop.

I happenned to bring the laptop at work about two months ago, and I didn't have this behaviour, I just noticed a few issues when scrolling fast. The laptop was in a cold environment, which makes me think that this issue is still related to the temperature of the system.

I took the laptop apart a year ago to clean it up (which lowered its temperature a lot) but this doesn't change anything now. So I would like to know if adding some thermal compound both on the graphic card and the CPU could fix this issue, or if such a behaviour usually means that the GPU is dead. Otherwise, what other solution do I have?

Here is a picture so you can see what it looks like : https://dl.dropboxusercontent.com/u/7890...

Thanks