USE THE WALL A/C CHARGER. Do NOT plug into a PC USB port.
Give it 1 hour minimum, 3 hours optimum, and some say 8.
The PC USB port queries the USB device to pretty much say "Hey how much power do you need?" If it doesn't get an answer it never puts out more than a very very small charge -- NOT ENOUGH TO CHARGE YOUR DROID.
If it gets a valid answer it will raise that power to anywhere from 100ma to 500ma and actually charge your droid slowly. THIS DOES NOT OCCUR UNTIL THE DROID IS FUNCTIONAL.
So if you're
- In "M" screen
- In "SPRecovery"
- Flashing ROMs
NO CHARGING WILL OCCUR.
So if you think you've "bricked" your phone because you did any of the above and it won't boot... charge with the WALL charger.
CHARGE WITH THE WALL CHARGER.
Your phone is fine.