USB Stick does not appear in WinExplorer as drive: How to show/enable drive letter?

I bought a new USB stick with 4GB and plugged it into a free USB slot on my motherboard.
In contrast to other USB sticks the new drive (letter) does not appear in WinExplorer (under WinXP)
even not after a couple of "refreshes".

However on other WinXP computers the drive letter appears without problems.

Furthermore I can access the drive by command prompt (on the first computer).

So what is the problem of WinExplorer with not recognizing the USB stick?

How can I force WinExplorer to show up the USB Stick?

Michael