Can anyone help me with my phone problem?

Hello there. I have an LG KE970 Shine phone. I have a small problem...I downloaded a ringtone for my phone to my computer. I plugged the phone into the computer so I could transfer it across, and all of a sudden, when I unplugged it from the computer, the phone does not recognise the carriers network. All it says at the top (I dont know if you have used this phone, but along the top of the screen where it has the battery and time, it has the carrier your with) all it says it wireless off. The phone works perfectly apart from that, there is not a thing wrong with it at all.

Do you think I should take it to a repair shop, or the carrier or what?