New motherboard, now CPU goes to 100% and crashes

[Terry2012]

I bought a new computer case and changed the motherboard at the same time.  Before, under load (for example playing Battlefield 3 even at Ultra settings) I had no problems.  Now, with the new MB, the game crashes within a few minutes.
I used OCCT software and it showed the CPU going to 100 percent and staying there.  I don't know if that is the problem, but the only difference is the new MB.  I had to underclock the two graphics cards (from factory overclock of 900/1050 down to 775/1000) and overclock the CPU using Smart 6 to 3.0, and even then I could only play at Medium settings with AA off.  I tried changing the affinity to use processors 0, 1, 2, 3 instead of 0 to 7 and that actually helped a bit; I could play Medium with AA on.
The temperatures were CPU about 75 and GPUs about 70, with GPU usage about 75 percent.  With the new motherboad and only one card, I could play on the High setting with AA.  But I have two cards and want to use them.
Does anyone know what I can do?
Specs:
MB Gigabyte X58-USB3
i7 920
9 GB RAM
Two HD 6870 2 GB in crossfire
Windows 7 32 bit with third party fix to allow more than 4 GB RAM.
(It allows you to boot to normal W7 or modified and I tried both and they would both crash.)

[Fatman]

OCCT software is designed to check your CPU for OC stability, so of course it is going to run att 100%. No point testing an O'C at only 60 or even 80%.

Are you O'cing your system? If so how, through bios or software? I wouldn't use smart 6 as I have found it delivers more problems and is buggy.

Have you tried to bump up your voltage on your Processor a notch? Say to 1.30v or 1.35v to see if you get stability?

You could raise the QPI/VTT vcore to 1.3 and the IOH core to 1.2-1.3 and see if that helps.

[Terry2012]

Thanks for your reply.  I didn't mean I ran the OCCT load test.  I was just looking at the monitoring section, not running the test, just monitoring the cpu usage as the game was playing.  Just normally it ran 100 percent.  When I underclocked the gpu and overclocked the cpu, it showed cpu usage at about 80 percent and I didn't get a crash.
I did use Smart 6, but I'll try using the bios and upping the voltage.
I was wondering why things changed with a different motherboard.