I assume you have installed the CPU correctly
Have you made all the required power connections?
Main Power: 1 x 24-pin ATX main power connector AND 1 x 8-pin ATX 12V power connector
Video Card Power: two 2x3-pin connectors, OR one 2x3-pin and one 2x4-pin
The AMD Phenom CPU memory controllers are only rated for DDR3-1333 but AMD says anything higher is at your own risk. By default your motherboard should be reducing anything higher to this speed. You can go higher if you set the speeds manually in CMOS. In case the CMOS was set to some settings that are givings problems now you might try clearing the BIOS to default settings.
If you are using two sticks of RAM you either have to have them in Slots (1 and 2), OR (3 and 4).
If you are using anything higher than DDR3-1866 like you had with your first set of RAM you have to put them in Slots (3 and 4).
Have you tried one stick of RAM at a time?
A Google search showed several people have had bad RAM or bad RAM sockets cause three long beeps.
BTW, from page 108 in the GA-880GA-UD3H User's Manual:
Q: What do the beeps emitted during the POST mean?
A: The following Award BIOS beep code descriptions may help you identify possible computer problems. (For reference only.)
1 short: System boots successfully
2 short: CMOS setting error
1 long, 1 short: Memory or motherboard error
1 long, 2 short: Monitor or graphics card error
1 long, 3 short: Keyboard error
1 long, 9 short: BIOS ROM error
Continuous long beeps: Graphics card not inserted properly
Continuous short beeps: Power error