When you open "My Computer" it accesses ALL attached drives, including ones it thinks are attached but perhaps are not, and ones that are having access problems.

It sounds like you are confronting either a timeout problem accessing a "drive" that is no longer connected or one you are having access problems with.

If you are connected to a network and have a mapped drive letter to a network machine then this may also be a comms problem.

First suggestion: Reboot - preferably a full power cycle (assuming you haven't already)
Second suggestion: Remove all removable drives (external USB drives, thumb drives, SD cards etc.) Don't forget that MFC with the memory device slots...
Third suggestion: Be patient, open My Computer and try accessing every drive letter - if one is slow to respond you have probably identified the problem device.

--=-- My credo: If it's worth doing, it's worth overdoing - just ask my missus, she'll tell ya laugh --=--
You're only paranoid if you're wrong!