Drive recognition problems...are usually indicative of either connection or drive/file system problems.
I'd take a look in Event Viewer for any errors
that specify any drive, as a start. They usually stand out (at least, mine do
) because the source will probably be "disk" on the System tab. You can sort the column by clicking on it and easily see any items thusly reported.
How To Use Event Viewer - http://www.bleepingcomputer.com/forums/t/40108/how-to-use-event-viewer/
If you have any...double-click on the individual line item for the most recent and post the detail.