PC won't recognize both my iPhone 4s

I have two iPhone 4s and both are no longer recognized by my HP desktop. I was able to do a back up on both last month but now when I go to the Device Manager they aren't even listed. There is no error or any sign that they are connected. I am connecting to a USB on the back of the desktop with the original cord and have tried all the troubleshooting listed here http://support.apple.com/kb/TS1495. I am at a total loss of where to go from here.