Computer Reboots Without Warning

Recently I purchased a computer from a friend for relatively cheap. It had good specifications and it worked well.

GA X58A-UD3R Motherboard
Intel Core i7 2.8 GHz
4 Gb RAM
Nvidia GTS 250
750 Watt Power Supply

The computer did not come with any drives, so I bought:
120 Gb SSD
1 Tb HDD

That day, I also decided to buy a graphics card, but to my disappointment, there were not enough connectors to power it.

A couple days ago, I ordered an upgraded Power Supply, this time 1200 W. It had all the right connections for this graphics card, so I installed it.

The graphics card was a GTX 680 Super Over Clock. The thing barely even fit inside my case. But, whenever I try to play a game, after about 5 minutes, my system reboots without warning. This, as you could probably tell, is extremely frustrating.

My first guess was that it may be the PSU or the GPU causing these problems, but upon further investigation, another possibility came to mind. Perhaps it was the motherboard. The BIOS for the Motherboard is outdated, much older than the new card. It dates back to the 20th April 2010. The Nvidia 600 series started their release in 2012. I am lead to believe that the card is incompatible with the current version of the BIOS.

I am considering taking this to a computer store to get it sorted, mainly because I lack the expertise to fix such problems myself.

The computer only reboots when I'm playing games. Games like:
ARMA 2
Borderlands 2
Red Orchestra 2
Planetside 2

But when I played games that were less "Graphically Intensive", the reboot issue did not happen. These games were:
Warframe
Team Fortress 2

So, I looked into the reports and it said that my computer lost power. I looked around the web and found that even for people who replaced their PSU still encountered the problem where Windows reboots for no identifiable reason.

For the games I was able to run, I was able to run them on full video settings with the GTS 250. So, the computer's processor and motherboard may be under new load, considering I am now able to run every game I own on Very High settings with this GTX 680 SOC.

When I got the card, I instinctively overclocked it. That may be where I went wrong. But these problems occurred when I started to play the higher graphic games with the overclock.

It would be very, very disappointing if my graphics card were the issue, especially since I spent $540 on it. So, if anyone has a solution before the weekend, it would be sincerely appreciated.

I intend on seeing an expert by the weekend, so fingers crossed for an answer. I don't wish to be set back even more money.

Once again, my CURRENT specs are:
GA X58A-UD3R Motherboard
Intel Core i7 2.8 GHz
120 Gb SSD + 1 Tb HDD
4 Gb RAM
Nvidia GTX 680 SOC
1200 Watt Power Supply

I eagerly and optimistically await people's replies.

El Presidente

Guys, thank you greatly for bringing it to my attention. I did some research and discovered that this brand of PSU is made cheaply. Some people said their computers ran slower, which now that I think about it may be happening with my computer now. I only hope I can return it and find one of a better brand. I will leave this thread open in case someone thinks of another possible solution.