IPhone will not connect to my computer?

So last week I flew down to Texas to visit my sister and nieces, and while there I ended up needing a passcode for my phone to lock my niece out of it since she's always nagging for it. However, after a little while I changed the passcode and when I came back to my phone later, I forgot the passcode. So I ended up being locked out of it and had to take it to Apple where they had to reset it to factory settings, everything was deleted. While there the only way I charged my phone was from a wall outlet, never with a computer.
Since returning from Texas, I went to get some of my music back onto my phone when I realized that it wasn't connecting to my computer, I moved the cable to different USB ports and everything, I even switched out the cord; it still wouldn't connect. I also noticed just today that a message is constantly popping up asking me for my voice mail passcode, which I don't even recall having a passcode for that. This message never started popping up though until today, two days after returning from Texas and probably five days after it being reset.
I don't even know if any of this has to do with the issue itself, but I just wanted to include the details just in case.

I don't think it is a problem with the phone, though you should contact apple. I think the problem is with the computer. Try connecting to a different pc. If that works it's the computer. If it doesn't, call apple for an appointment