My 5800 dies off once in awhile. Even when the battery is fully charged.

Usually happens when:

I record video for more than 10 minutes.

or

When I'm driving long distant using GPS. (I normally plug to charger)


And when I try to on back, it'll show that NOKIA logo for like 30 seconds, then will off again. Have to on like 8-10 times only will on properly.

And the phone will be hot.

How come???