i've got a problem with my Nokia 6680.
A week ago it started to ignore some number keys becoming unusable. I coldn't backup the data (due to lack of time), so I decided to use use another phone. I left my 6680 open with the battery.
Now, it doesn't start up. The display lights up with the Nokia logo only when i plug the phone to the charger. I changed the battery, pushed the 3*power etc combination, but nothing happen.
It doesn't sound good and you seem to have tried everything already. Next step is to send it to a Nokia Care Point or get a new phone.
You can find your nearest Nokia Care Point at:
http://www.nokia.com select your country, go to the support section, then select repair.