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The problem might not be related to the RAM; use the first 2 DIMM slots, skip, and last slot as shown below and not DDR3_4.
CPU | RAM | RAM | blank | RAM |
CPU | DDR3_2 | DDR3_1 | DDR3_4
| DDR3_3 |
The Primary DIMM Slots are DDR3_1 & DDR3_3. However it is ideal to use 2 or 4 sticks of RAM since you have a Dual Channel MOBO. Further, ALL sticks MUST have the same Frequency, CAS Timings, and Voltage. Different sizes in the White slots is not recommended.
You can test this by pulling one stick and use the WHITE slots only.
CPU | blank | RAM | blank | RAM |
Next, it might be a good idea to Clear CMOS using jumper method; see page 30 of your manual. Further, often a BIOS Flash can correct the problem; use the Q-Flash method.
GA-P55A-UD3 (rev. 2.0) - http://www.gigabyte.us/products/product-page.aspx?pid=3439#dl
GA-P55A-UD3 (rev. 1.0) - http://www.gigabyte.us/products/product-page.aspx?pid=3242#dl
Q-Flash procedure - video:
Part 1 - http://www.youtube.com/watch?v=UCCId1Mcrw4
Part 2 - http://www.youtube.com/watch?v=Qlx5GBkiaM0
Part 3 - http://www.youtube.com/watch?v=EX78S4qyHu0
If running XP see -> http://support.microsoft.com/kb/326676