p990i switchoff problem

dear
my p990i is remain on but to callers system says my phone is switched off. problem is started almost ten days before. after that i installed new soft. from sony ericsson website, but not fruitfull.
when it is told to be switched off, the signal bar showes full strength, but gprs signal disapear. on restarting the phone problem resolved for almost 10 to 15 hours.

thanks
प्लीज जल्दी जवाब दीजिएगा

My S.E p990i i turn it on but it hungup wen loading sony ericson welcom note. thanx