Run a MEMTEST (google it) to soak test the RAM.
Re-seat the CPU? Check that all cables are connected, all cards and RAM are fully seated.
Socket 939 is a few years old now - you'll struggle to get another identical board new, though you might find a refurbished board from lambdatek, or on ebay as you say.
Search for socket 939 boards from ebuyer or whatever your favourite supplier is - you can probably get a different 939 board and transfer most or all of your components over, though you'll probably need to do a complete system installation from your original media.
SD