Why does my xbox live gamer tag mess up during a game?

I start up my xbox 360 and sign in and every thing is normal but a soon as i play a game my xbox thinks that i have no gamer score and that i don't have any achievements and that sucks so can someone please help me i have 10000 gamer score and don't want to lose it.!!Why does my xbox live gamer tag mess up during a game?although yahoo answers many questions, in this case it would be better to call the company and see what they say