After starting bitmonerod.exe it synchronizes with the network for some time till it tells me that it is synchronized and I can start up simplewallet.exe
You can try deleting/moving your binary wallet file (default name wallet.bin) and just keep your keys file (wallet.bin.keys), and then let simplewallet rebuild the binary file. If you're moving a wallet file from 32-bit to 64-bit this can definitely be an issue, also moving from *nix to windows I think.