After updating your system specs, as Britton30 suggested, be sure to include the make and model of your PSU.
If you are having trouble with Crossfire, disable it and remove 1 card and run the gmes again and see what your results are. You may have to lower your settings some. Whether that card passes or fails, remove it and put the other card in and play the games again to see what happens. It is possible that one of your cards are bad.
Also, download GPUz. Post a screenshot of the main tab and the sensor tab. Do the same with each card when you install them one at a time. If you do get crashes, Create a folder on your desktop and name it whatever you want. open GPUz and click on the sensor tab, at the bottom is a checkbox called 'log to file', check the box. As soon as you check it a dialogue box will appear. Browse to the folder on your desktop you just created and select it. Then play the games again until they crash. It will record all info about your cards. Zip the folder up and attach it once you have finished.
But, it is important to do as Britton30 suggested and give us your system specs. It will help us to help you.
Plus, if you are overclocking anything, please set it back to default values. And also, please go to BIOS and give us the readings for your +12V, +5V and +3.3V.