WinXP keeps not seeing USB connected external hard drive.

I have an unusual problem. Some time ago, I got a USB connected 250G
external hard drive that I use only for storage. My WinXP system has got so
used to it that it thinks it's a regular hard drive instead of "removeable
media."

The problem is that here in the past few months, my system randomly decides
that the drive isn't there at all as if it's unplugged. Any Windows Explorer
window showing any folder on the drive closes. Any program such as a web
browser that last saved something to that drive goes to the default folder on
the main drive if I try to save something. If eMule is running, any file
that's downloading gets a "error" and my comp gives an error beep. If
Visipics (duplicate image detector) is running, it thinks the job is done.

To restore the connection, usually, I unplug the connector from the USB port
and plug it back in. Sometimes I have to restart my system.

The external HD I have now is a HP Pocket Drive that's entirely USB powered.
I suspect that if I were still using the Lasonic 250G USB connected drive
that required an external power source, the problem would still be happening.

Once in awhile, the same type thing happens to my mouse and keyboard, both
of which are connected to the USB port next to the external HD's port through
a USB hub. They quit working or proper operation is spotty. Proper
operation is restored through unplugging the hub and plugging it back in and
once in awhile, a restart is required.

Anyone have any idea of what's causing this, how to fix it and how to
prevent it?