First double check whether the black slot is working properly or not.
Insert only one memory module on black slot and check.
Secondly, please try the following steps:
Go to BIOS > Perfomance Menu > Watchdog Timer > Disabled.
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From page 14 of the manual:
DDR3 1333 or higher memory support on this desktop board requires
compatible XMP-enabled memory or advanced knowledge of BIOS and
manual memory tuning.
Is this memory XMP-enabled?
From page 71 of the manual:
3 beeps is the code for "no memory"
If the memory is XMP-enabled compatible then perhaps you have to do some manual tuning to get it configured.
Page 38 and 39 of the manual show you the details of the four sockets.