I actually have the exact same thing going on. PC worked fine for about a week after i upgraded it, my current setup is:
Gigabyte 890FXA-UD5 (Rev 2.0)
4gb PC 10600 Corsair Ram (CT2KIT51264BA1339)
650 watt Corsair PSU
EVGA GTS 250
AMD Phenom II x6 1090T BE (@ 3.2ghz, stock speed)
When I power on the PC all the fans spin up, HDD's spin up, DVD drive checks for a disc, etc - Then I get 11 beeps from my system speaker. Much like the problems OP had.
I have, like OP, disconnected every peripheral from my PC. I have disconnected everything that is not necessary from the board, leaving only the CPU (and heatsink), RAM, and Video card connected to the mobo. Hell I cleared the CMOS with the button on the mobo (after the PC was powered down and the power cable disconnected). I even pulled the CMOS battery before I went to bed, woke up this morning and popped it back in. I have tried cycling both of my ram sticks through all 4 slots one at a time, all of which gives me the 11 beeps. The only time I get a different beep code is if I try to boot with no ram, then I get 12 beeps. I still get the 11 beeps, a pause, and then 11 more beeps, and a pause...so on and so forth.
Much searching through forums and various websites has not turned up any useful description of this beep code - only that it may or may not be a component of my computer that may or may not be working correctly. I have not had the chance to talk to Gigabyte customer service, as they are closed on sundays...
If OP is still watching this thread, did RMAing your board fix the issue? Or did you replace your ram?
Edit 1: Added a bit more description to troubleshooting and the cause of the problem.
Edit 2: This started as a system freeze as I was closing programs to turn my PC off for the night. I shutdown my media player (SongBird) and the system hung right there. I waited a couple seconds to see if maybe it was just some odd hardcore lag or something, but this wasn't the case. After about half a minute of waiting my system responded, but with horribly distorted audio that appeared to be stuck in a 5 second loop. I performed a hard shutdown and when I tried to reboot, I started having this problem.