I assume your Thermaltake 750w power supply is a TR2?
Thermaltake TR2 is one of the worst power supplies on the market and it's not even priced with the other junk. So not only do they sell you junk they rip you off for it.
The 2 best power supply review sites are Hardwaresecrets and jonnyguru. Here is the Hardwaresecrets review of your PSU. The whole article is worth reading but here is the conclusion. http://www.hardwaresecrets.com/article/Thermaltake-TR2-RX-750-W-Power-Supply-Review/902/9
Here is a very good ( not perfect but very good ) tier list. Notice the TR2 and TR2 RX are tier 5. The do not buy under any circumstances and replace ASAP if you do have one tier. http://www.eggxpert.com/forums/thread/323050.aspx
Thermaltake and Coolermaster are 2 companies that shoud not be in the power supply business.
For quality stick with Corsair, Seasonic, PC Power and Cooling, XFX, Silverstone, Enermax, OCZ and Antec.