Hi,
First, check with HP or find a data-book to make sure that the ethernet adapter in the printer is working. From the descriptions, it sounds as if it’s dead.
Next, make sure that Ethernet interface cable you are using is 1) “cat 5”, 2) that it is working properly. I've come across cases where a cable may work in one instance but not another. This is sometimes due to the cable being crap and sometimes due to the interface where the cable connects being crap, and on rare occasions, both the cable and the connectors are crap. I've had other instances where the cable does not work at all.
If you have a good ohm meter and the right contacts, you can check connectivity on pins 1,2, 4 and 6. If there is any variance at all, between the connectors, toss the cable.
Next, if you are going to go more than about 6’ for USB, you should use a so-called “Active USB extension.” Here is a link to a suitable cable,
http://www.amazon.com/Tripp-Lite-U026-016-Certified-Extension/dp/B0002D6QJO. With typical or passive USB extension, the signal degradation makes more than about 6’ ill advised. I think the USB spec says you can string up to 4 active USB cables together.
Next you can get a device that is a USB print server. This has an Ethernet connection on one end where you connect the print server to your network and a USB connection on the other, where you connect your printer to the print server. Note that not all USB printers get along with this kind of print server. These are generally a lot less expensive than buying HP’s print servers. Read the compatibility chart and call the manufacturer if there is any doubt.
Last but definitely not least, you can order a replacement for the ethernet/USB interface device in your printer directly from HP. This is the best if probably the most expensive solution as you’ll side step all the work around related problems if you go this route. Once you are 100% certain that the problem is not due to the ethernet cable or connectors, this what I would do. Everything else is merely a penny-wise solution.