Well, you need to go through the "numbers" as it were.
First, was your phone ever seen by your PC? If yes, when did it stop?
Have you tried the following:
1) rebooting both Phone and PC.
2) changing the USB port
3) changing the cable.
4) connecting to someone else's PC to see if the phone is recognized there?
5) uninstalling and then re-installing iTunes (this requires extra instructions, because there is more than just iTunes to uninstall if you have to try this)
Lets start there and see if we can get you going again. If none of this works, there might be a different problem going on.