Very frequently, when I try to send text messages or make a call I get a message stating I have an "Invalid Sim Card." I...

Abigayle, This could be caused by a number of reasons. Try these first: 1. Plug the phone into your charger for 10 minutes. The phone could be drained of battery and this will provide enough charge to power on. 2. Try purchasing a new charger (Mini USB). Your existing one could be faulty or malfunctioning. 3. Still not powering on? Unfortunately batteries malfunction and eventually need to replaced. Go to your service provider’s retail store to purchase and install a new battery. If the phone is still not powering on you have a problem. The phone itself may be defective. Time to start shopping for a new phone! Good luck!