USB and Flash Drive

I have two Dell PCs each with WinXP. I am trying to use a USB 2.0 portable
flash drive, Ativa, 512 MB that's produced by PNY Technologies. PNY flash
drives are listed on the Windows Hardware Compatibility List at the Micorosft
web site as supported for WinXP.

When I plug in the flash drive and open Windows Explorer, no new drive
appears. I restart and still no new drive appears. In device manager, I
expand all items and cannot find a description that sounds like a flash
drive. I remove the flash drive, restart, open device manager and again
expand all items. The list of items, with the flash drive removed, is
identical with the earlier list with the flash drive plugged in.

For the 2nd WinXP computer, I plug in the flash drive. It does not appear
in Windows Explorer.

Any suggestions on steps I can take?

Thanks.

James