ECS *the board maker* policy and almost every seller will not take back a part with physical damage. So, while I know this will -really- piss you off, you basically just ate a motherboard. Don't blame them, though.. Asus, Abit, MSI, Gigabyte, FoxConn, etc.. all of them will reject warranty returns on what they view as "physical damage"
The good news is that 650i motherboards are not that bad. I don't know where you bought parts, but if they have any sort of RMA system, they will reject your return as physical damage.
Now, if the 4 pin came just unattached, normally you wouldn't get this.. if it's -partially- unattached, then you would get a grounding issue on the 3V rail, which means outside of your board, I'd be very suspect of the RAM in the system, and before you rely on it, I'd run a memtest 86+ on it.
I don't think there is anyone you'll call who will help in a warranty sense, I think you're just going to buy a new motherboard.
EDIT: I see you powered it up again after you got smoke the one time. I'm hoping main components (CPU, Video Card, memory) were not installed when you did that.