I know it's real easy with CPUs to get one of the 4 corners not fully down which makes for very poor heat transfer. I can't see your work but you'll need to have heat sink surface flush on top of the GPU and perfectly parallel. You didn't mention whether it had a fan. If so, I'd wonder if it's working properly.
My wife's GeForce GTS 250 started running really hot a few days ago. Nothing to bad in nonGPU intensive games, like DCUO, but whenever she loads up Skyrim or SWTOR it shoots into the 90s before very long. Well it used to stay in the 70's under load, and 90c is a little hot for me, so I decided to clean it out. I've never opened a graphics card before, but it wasn't too hard. I cleaned out ungodly amounts of dust and cat hair from the air intake of the GPU, so I'm guessing that is what caused the overheating.
Well, I cleaned the old thermal compound off of the GPU and heatsink, then put on some new stuff (just the radio shack brand that I had lying around). Everywhere I read told me not to put too much on, so I put on barely enough to cover the GPU, even though when I originally opened it the compound was EVERYWHERE, like they had used gobs. Well, I immediately closed it back up, threw it into the computer and booted up. I use EVGA Precision to monitor temps, and when she went into SWTOR it shot into the 100's almost instantly before I pulled the plug.
Should I apply more thermal paste? does it need to sit for a while after application before use? Is this card just trash?
Thanks in advance, Billy