Hardware

See if your scanner still works with Windows 98 -- it may be that the hardware (the scanner) has developed mechanical problems. When is the last time you successfully used it?

Make sure that the USB ports are working.

You can check in BIOS settings, and device manager.
Better yet, verify that the ports function with another USB device.

Windows should recognize any USB device as soon as it is plugged into the USB port.

A couple of other things to check, did you install the driver before connecting the scanner, and then re-boot?
While USB is suppossed to be plug n play, most devices that I have installed require that the device driver be installed first.

Is the scanner powered up?

Some systems do not provide enough power on the USB ports to operate all but the simplest devices. Try connecting the scanner to a powered USB hub.

A final idea is that the USB drivers for the new PC were not installed, or have been damaged.
Try re-installing the system USB drivers.

Chas

Thank you both for your advice, but I have a few points to add. The scanner is in full working condition, as I have successfully used it on my old windows 98 system.

Unfortunately, I have no spare com ports, so on my new system it is necessary to use USB. When I have plugged the scanner in and turned it on, I am notified in the task tray that the device has been detected, and that windows needs to install the hardware. According to the setup program, the drivers should have been installed. But windows cannot find them. I have tried installing the automatically, but this did not work, and when i tried to locate them myself, the wizard requires a setup information file. Neither the two .inf files in the HP download folder will respond to this. This seems i nuisance, because i know the name of the driver, and where it is located!

I have run the setup program several times now, each time it reports that the drivers have been installed. I have rebooted as it has instructed me, but this has not worked.

Sorry for not getting back to you sooner.

Since you have a new PC, you need the full 30.65MB download from HP.
http://www.hp.com/cgi-bin/cposupport/swindex.pl?p=hpscanjet420512&l=en&c=MicrosoftWindowsXP

Remove any spaces from the pasted link.

Start with the scanner connected to the PC.
Uninstall the scanner in device manager.

Shut down, and disconect the scanner.
Re-boot, and run the install for the program.
You will likely end up extracting the program and running another program.

After the program installs, re-boot as required. then connect the scanner to the USB port.

If you still have problems, you may need a Windows update file from Microsoft, or a driver update for the USB port on the PC.

Chas