MY HP SCANNER MODEL4400C

1. Is the scanner plugged into the USB or Parallel port?

If USB, are you running at least Windows 98, and is the USB port enabled in BIOS settings.
(You can check this from device manager, just expand the system devices branch.)

If Parallel, is the port set to ECP/EPP mode in BIOS settings?
(Again, you can check this in device manager. Expand the ports branch, and verify that the properties for the printer port identify it as an ECP/EPP port.)

Also, if parallel, is the printer connected to the scanner?
For many scanners connected to the printer, the printer must be turned on for the scanner to function.

2. Check for any transport screws that secure the scanner mechanism for shipping. These would lock the mechanism, and cause the scanner to not function.

3. Check the scanner power supply. It should get warm, but not hot. You may be able to feel a slight vibration when you touch it.
If you have, and know how to use a volt-meter, verify that the power supply has the correct output voltage. With the scanner disconnected, the voltage may be 20% - 50% high.

4. The scanner may be bad.

Chas