Ummm... well one of your problems could be that your cpu privite cooling might not be good enough or maybe your graphics card canot handle the games you try to play or it could simply be that the cable to your moniter might not be propily pluged in.
Find out how manny watts your psu can supply then find out how manny watts the gpu and the cpu require combine them then just add 100-150 more watts foranything else and if you still have more watts to use then tahts not the problem but if you've run out of watts then you have your problem
And are your airways clear? i mean does you computer have clear ways for air to escape that can seiriesly heat up you rig and cause it to crash!
hop it helps!!!