Problem with computer recognizing external drive

From time to time, my external drive is not recognized by the computer. Just a few minutes ago, I had to uninstall and reinstall the external drive. This has already happened several times, and I was wondering if the drive is going bad or if the USB universal bus controller is going bad? I have two other devices connected via USB (printer and digital video converter and so far no major issues with the two. But, I had several pop-up windows while printing saying that it would print faster if connected to USB 2.0. I have an Asus P4G8X Delulxe motherboard and all USB ports are 2.0. Any ideas of what might be going on? Is there a diagnostic utility to check for problems? TIA