Almost same here

Last few days my browser began to stutter if I had opened some more windows and sometimes it felt like battery drains very fast/getting warm without any usage/visible programs running.

Tonight I was online, never saw that before, at one time my N900 completely rebooted without any press on powerbutton etc., and after that restart my telephone-function does not work anymore - it does not find my provider anymore!

Whatever I to, connect to provider isn´t possible anymore, already removed battery and restarted again, without change. If I want to select provider manually, it shows my provider, but I am not able to connect to (normal 2G)!

Is it a virus probably? Do I need to reflash anything or is there any way to find out what is going on inside my software?

What can I do now?