IPhone 4 won't sync on computer or iTunes?

I got an iPhone 4 flashed to Metro PCS about 4 months ago. While on another computer, my phone synced to iTunes just fine. But now, I keep trying to sync it to my home computer, using Windows Vista, and it won't sync at all. It won't even register the fact that my phone is plugged into the USB port. I just updated my iTunes, but still had no luck.

Did you update to the current version of iTunes?