Well deez, from what you're telling me about the checksum there must be something wrong with the apple_os.bin in the flash memory of the player. The one solution that is sure to work is using itunes to restore the iPod back to factory settings. I'm not sure but I think that when you ran ipodpatcher, there should have been a backup made of the apple_os.ipod and it should have been put in the same folder as ipodpatcher. If you happen to have the apple_os.ipod, place it in the root of your iPod and the bootloader should grab that one when it's told to start the apple os.
If you don't know, you can connect your iPod to the PC still, you just need to hold play and centre on boot when you see the apple logo (before the rockbox bootloader kicks in).
hope that helps.