The iPod or thumb drive that I plugged is visible in device manager but not visible in my computer. I clicked at disk management and waited for long time but it just showed connecting to logical disk manager service... I didn't see any drive listed. How to solve the problem? Thanks

You should install USB 2.0 driver or the drivers that came with the iPod. You can download drivers for here

Scan your computer for virus and try to reconnect it again