my n-gage qd won't play 3gp files

Dear Symbian users,

I own a N-Gage qd. I use to convert my divx's to 3gp (both with linux and Windows). I don't know why, but after 5 seconds the player (whichever I use) stops saying that it's impossible to play the file. With the same phone and the same files all worked till 4-5 days ago.
Can I reset the system ? Or what can I do ?

Thanks