If your computer is a prebuild (Dell, HP, etc), then there may not be too much you can do in the BIOS. On the other hand, if your computer was a home build, then your BIOS should be able to raise the limit of 50°C.
I took a look at your mobo manual. I don't see an option to change the shutdown temperature, but you'd be the better judge of that. Check the Advanced section of your BIOS, under H/W Monitor. If you can't find a way to raise that limit, then perhaps the alternative would be to set the fan speed to 100% when your CPU reaches 50.
It's possible. In my opinion, 50°C is oddly low for your computer to shutdown on. The mobo has the thermal sensors, and if one of them is bad, it could be only reporting 50°C, but in reality, your temp could be higher. Still, even that is a stretch, because to reach a thermal shutdown temp, you'd have to be doing some serious OC w/o aftermarket cooling.
Where are you reading the temp at, the Hardware Monitor just before the OS loads?