Plugging in a USB device does not show up in My Computer. - Pan

I have searched the net and note various flavours to USBs not appearing in My
Computer. I have tried a lot of the recommendations to see if my problem can
be resolved, but alas no joy.

I detail below what my problem is, what I have tried and hope someone can
help to resolve my problem.

If I POWER UP the PC with the USB device plugged in, then it is visible in
My Computer and I can access it.

Once the PC is powered up, and I plug in a USB device, it does not appear in
My Computer.

If I right click My computer, go into Manage followed by Disk Management
then the USB device shows up with an allocated disk drive letter and Healthy.
Whist here unplugging the USB and plugging it back in make the drive
disappear and then reappear.

If I right click My computer, go into Manage followed by Removable Storage
then the USB device shows up with a Red Cross Whist here unplugging the USB
and plugging it back in make the drive disappear and then reappear.

I have also tried to re-install the drivers and even after that the USB does
not show up in My Computer.

My Pc is running:-

Windows XP;
SP2;

Any assistance offered would be appreciatred.