My N73 restarts and displays sim card not valid.Battery problems as well?should i buy

My nokia N73 asks me for the lock code,after i enter that,it asks the codeagain,twice or thrice.then it restarts or displays sim card not valid. the battery also runs down after a single call and phone switches off.i even removed my memory card but the problem persists. how to proceed?

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Was your phone like that since you bought it? I think you might need to return your phone to the shop where you bought it so that it can be checked. I hope your phone is still under warranty. Good luck!