Inspiron doesn't recognize Dell USB Devices

I recently purchased an Inspiorn 8600, along with a Dell USB memory key.  Originally, only one of my USB ports seemed to recognize my memory key (i.e., show it as available).  Now when I hook up USB devices to either USB port (my memory key or a USB mouse) they are not recognized and don't make the noise when I click them in.  I tried restarting my laptop with the memory key already attached, and still it is not recognized. 

I'm running Windows XP Pro, SP1.

Thanks for any help!

--Hilary