Computer does not recognize iPhone 4s?

I got my iPhone 4s back in October, and it worked just fine when syncing with iTunes and all that. Recently however, like in the last 3 weeks or so, whenever I try to plug it into the computer, my computer won't recognize it. It dings like I've inserted a USB, but it doesn't show up in "My Computer" or iTunes, and does not charge. I have tried two different cords. I tried plugging it in on my dad's Macbook, and it was recognized immediately, so I don't think it is the phone. I followed all the steps listed on the Apple technical website, and nothing has worked. I've restarted my phone, reset my phone, updated iTunes and restarted my computer, but to no avail. I have a Lenovo Thinkpad W510 and am running Windows 7. It charges just fine when plugged into the wall using the same cord. Other USB's work fine when plugged into the computer. Any advice or help would be greatly appreciated!