Phone [Q] Phone appears to have signal but won't receive calls/sms and -..

My phone(Galaxy Gio) appears to have signal(3G Signal all the lines are full) but I can't call or message anyone, nor vice-versa. I thought that it was the SIM card at first. I've tried other two sim cards that were working on my other phone, the same problem. It's some weird issue with the phone.Also when I plug in the USB cable the phone keeps connecting and disconnecting giving low battery alert.