When you say it was stuck during POST, can you remember what error message was displayed? The POST message may have simply been that the amount of RAM had changed and the computer wanted you to confirm it.
Nonetheless, if you really are stuck with 2GB RAM then you'll have to replace the motherboard. 4GB is quickly becoming the bare minimum for modern games. The extra expense of a new motherboard may put a hole in your wallet, but this would be an ideal opportunity to replace the processor as well.