P55M-UD4 QVL: http://www.gigabyte-usa.com/FileList/MemorySupport/mb_memory_ga-p55m-ud4.pdf
No Corsair listed for the speed rating (1333) of you memory.
Back to the basics:
First try running Memtest86+, this runs from a boot disk or CD and should eliminate or
confirm if your one or more of your memory sticks are bad or the SPD values in the BIOS are correct.
Let it run for as long as you can: 2,4,6,8 or more hours, if no errors by then your ram is OK.
If you have a copy of Windows XP around try installing it temporary (if not Windows 7 will work as well)
"No need to activate as you get a 30 day grace period which is perfect for testing"
and then use the following tools (this assumes the memtest shows no failures)
Prime 95:http://www.mersenne.org/freesoft/
It's a stand alone .exe file contained in a .zip archive.
Just choose to run the "stress test" option for 3 hours or more.
If your PC can pass this test both your memory and CPU
are fine (close the case cover to maintain proper ventilation)
JS
Never be afraid to ask. This forum has some of the best people in the world available to help.