Fastboot has a recovery option, but he said he tried and it stays in the bootloader ("fastboot mode").
To the original poster:
Hold the power button in for at least 30 seconds (until you feel the phone vibrate), then see if you can start normally. If not, you'll have to flash at least the boot.img file (if that's gone, you won't get past the bootloader - that's what the bootloader loads.) If flashing the boot.imng file still doesn't fix it, you'll have to flash the entire ROM, since it's no longer there. (But the "can't get out of the bootloader" problem [and a PC probably can't see the phone by running fastboot devices either] usually means that holding the power button down until the phone vibrates will fix it.)