The PSP 3000 was released in the U.S. on the 15th of October 2008.
when I play games,the character goes backwards when I'm not pressing anything
make sure you didnt' hold down said key when booting up your device. If it is still an issue,try to clean around the button with a little alcohol. If still no go, then you have worn out the button itself.
My analog nub gets stuck, definitely take off the case and clean it with some alcohol.