I let my Nokia 5800 run out battery completely, and now it won't charge/turn on

[RachelNevill]

again? I don't know what to do, and I don't know whether it is the battery that needs replacing or the actual phone?

[SaltUK]

If it was working before, and you have merely let the battery discharge, it needs an overnight recharge.

[Unregistered]

You may of put your battery into engineering mode which makes it only engineers can make it work. Just put it to overnight charge and it should work