Hey, stop here for a minute. Don't do anything with the fan-curve until this has been done properly.
First of all, check all the temperatures: CPU, motherboard, graphics card etc.!
It's absolutely the first thing to do, no matter what.
I suggest download HWMonitor Free version and make sure that You uncheck any third party s/w during installation.
Ok. Take the Zip-file it doesn't contain any third party s/w
http://www.cpuid.com/downloads/hwmonitor/hwmonitor_1.28.zip
Then unpack, start HWMonitor and start the most demanding game on Your PC.
Play for at least 15 minutes, quit the game and then take the readings from HWMonitor.
There are 3 columns:
the first Value - shows the actual readings
Second Min - shows the minimum readings
Third Max- and most important: it shows the maximum numbers the system has been up to.
But all columns is vital, since HWMonitor also checks all the voltage on every aspect of Your whole system, which can be important too.
You can click File > Save Monitoring data => and post it here, so we can take a look at it and then perhaps come up with some solutions or maybe further investigation is needed.
Best Regards from Sweden.
Ps. Sorry for my poor english grammar.