Was looking all over for this peep code. Getting suggestions of checking memory in different slots to trying to remount the CPU.
But specific solutions for this model of MB, I have not found.
Maybe try checking the CPU and see if its properly mounted. The only read I found that had a solution to four long beeps (same company, different model MB), solved their problem by remounting the CPU.
Here is this link: http://forums.tweaktown.com/gigabyte/37547-ga-ma78lm-s2-four-long-beeps-2.html
Sorry I cannot find info specific to your MB.