Help - S3 getting worse.

I bought my S3 At&t in india unlocked here are the problems i'm facing -

1. Main problem is I'm loosing signal frequently even my 2000Rs/30$ nokia gets full signal.

2. It connects to PC like in 1 in 1000 attempts,Sometimes it connects to pc as if it is connected to charger(no storage)

Help regarding these problems are greatly appreciated.Thank you !

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