This might be a long shot, but have you tried different USB ports?
I had a scanner that insisted on being installed individually on EACH
port (including a powered USB hub). After installing it "everywhere",
it works "anywhere"...

There is a USB ready program to check the software part of the OS.
http://www.usb.org/about/faq/ans3/

                                            Rick Glazier

From: "Walt Ezyk"
> Hi, in March my computer, PIII, 450MHz, 256B ram, Win98SE, crashed with the
> blue screen. A tech person restored the system and all is working well
> except the scanner. When ever I click the scanner icon to start up the
> scanner, I get the message "please connect or switch on your scanner".
> Before the crash, when I turned on the computer the scanner indicator light
> would blink and then remain on. But now when I turn on the computer the
> light blinks but then it doesn't stay on. The scanner is an Agfa Snapscan
> 1212, connected with a USB cable. I've changed the USB cable with no change.
> Is there a way to check the USB port? Thanks.

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