it does sound like the video card overheating. It could be that the heatsink has come unseated, and I think no amount of blowing will cool it down if that's the case. So you can try taking the heatsink off, cleaning it with alcohol, and putting it back on with some thermal grease if you're comfortable doing that, but then if you do it wrong you could kill it entirely so.. do at your own risk.
There might be a way to check the temperature with some software as you can do for a CPU.