Compaq Computer won’t recognize USB Flash Drive

I have a Compaq Presario 5340 that I’ve owned for a while now (since 1998), but it’s always worked okay with very few problems.

I had Windows 2000 for the longest, but I recently upgraded to Windows XP. Now, my desktop computer won’t recognize my SanDisk Cruzer Micro (http://www.sandisk.com/Products/Item(1922)-SDCZ6-2048-SanDisk_Cruzer_Micro_2GB_Black__New.aspx).

Why is this, and what do I need to do to fix this??

Thank you very much for any assistance and feedback!!

Alan