I noticed a problem, that I cannot play anything on my N900 Few days ago I could, now it does not play when it should. Nothing happens, when I try to change volume it says "Unable to perform operation"

In last days I installed and unistalled few programs:
external subtitles support
fm boost (still installed)
fm rds notify (still installed)
appwatch (still installed)
powatool (still installed)

and some more, which I do not remember.

Internet radio is not working, music player, video player nothing works, did reboot many times, nothing helps.

Any idea?
Thank you