Ok, so let me relate to you what happened with my droid:
A while back, I downloaded the froyo update. My droid lost power and got bricked on the M screen. I tried formatting it and wiping the cache. I rebooted... still stuck in the m logo screen. So I tried doing it again, and this time selecting "update.zip." Doesn't work. I am met with an error that says
E: failed to open /sdcard/update.zip no such filename or directory
E: Signature verfication failed
I want to put a new update file on the SD card, but I cannot recognize my droid through usb because I cant activate USB mode.
Is there a way to load update.zip using the bootloader mode?