Hello, I have been having this problem where my computer shuts off while playing games that you need a better computer to run. I recently bought a GTX 550Ti GPU and a 700W Power Supply. I'm not sure what the issue is but if anyone could help I would be real appreciative.
The question is, did you buy a quality branded 700W power supply, or just buy one for £20 or £30 pounds thinking it would do. Please list the brand name of the PSU.
More than likely a cheap PSU, over rated and no where near what it says in wattage or amp output to the 12v power rails.
Reset the bios and have the ram cards placed correctly, generally 2nd and 4th for two cards. Also make sure that you have made the right settings in memory timings and voltage
If all fails try updating your bios.