error 16 is a special dashboar error it is when you leave your xbox without power for more than 5 hours after error 13/21 and your clock runs out of power. and so when booting your xbox would normally give you a dashboard so you can reclock your clock but as you have no dashboard wola error 16
once you get error 16 you can no longer boot disks this is because your xbox does the following on boot ups:
Boots --> checks clock --> clock has no power --> check hard drive for dashboard ---> no dashboard --> servicing error 16
The only way to fix it is with hotswap or a modchip.
if you do not have any-back-ups you are going to find this part extremely hard. No eeperom back-up and ur practically raped. I would personally use xboxhdm found in the usual places and refromat your whole xbox either with pirrups hotswap if you have no eeperom or if you do its easy to fix. use the following link
http://xbox-hq.com/html/xbox-tutorials-161.html
if you have an eeperom back-up put it into the eeperom folder within xboxhdm contents and fixing your xbox will be a doddle
