I had the same thing happen to me. My N900 is an alarm clock now with poor battery life (I imagine the battery needs replacing).

Just ditch it and get an N8 or E7 and cross your fingers that this whole QT thing and the upcoming changes to symbian will make the symbian OS more user friendly.

As soon as I updated to the most recent firmware on my n900 my device started slowly failing to maintain 3g on tmobile until i finally got the sim card symbol with the red line through it and the notice that all telephony functions have been disabled.
I decided after trying many things that it was bad soldering between the sim card reader and the mainboard and I just gave up and bought an N8.
Boy am I happy with the N8 hardware and the extras like wifi N and 5band 3g and gorilla glass and dolby surround sound this is a nice phone but I'd prefer a hard keyboard so I'm seriously considering buying the E7.

Browser on N8 sucks balls like seriously. I can't wait for the next symbian update. They've been releasing minor OTA updates recently for N8 instead of one big update like with N900 so that's also nice.
N8 processor is slightly slower than I'd like. I'd like to see a 10 to 30% increase in speed. Since symbian is open source now I'm hoping we can overclock it.
Another stupid thing about N8 is the "message deleted" popup totally covers the subject and sender fields of your next email that you are reading so you have to wait for 5 seconds until it disappears and apps will once in a while just suddenly close on you or move to background.