Wireless Access

My company has a number of the HP4600DN printers running on a Windows 20000 IP/Novell IPX network and we have recently come up with a problem with the Jetdirect 615n (J6057A) 10/100 card. The printer quits printing. Sometimes power on/off reset will restore operation but recently this would not work on two of our printers that seem to have the same problem. Symptoms: Jetdirect not seen on network by IP or IPX - no responce to ping either.
Unable to print (not even test page).
Printing configuration from the control panel only prints only the first of two pages - the second page contains all the network settings.
On both printers there was no link light and the network cable/connections tested good with with test equipment.
Jetdirect cards appear to be dead or not recognized by the HP4600DN - have even cleaned connectors on cards and reinserted them.
The confusing part of this problem is when I brought them in from the field after replacing them with new boards.
I powered down my local office HP4600DN and inserted one of the dead cards. It worked! I ran it through manual and auto configurations and could not get it to fail. The same was true with the other 615n card. It worked too.
I have read on another part of the forum that others have experience this phenomenon by taking supposed broken jetdirect cards and letting them lay around on the desk a couple of days and they fix themselves? Could this be a thermal intermittant problem that could be a manufacturing defect common to the jetdirect card? And could it be the card problem could have been fixed in the field if I had just performed a factory reset to defaults on the card? This is a strange problem we are experiencing with the 615n and at over $300 a card and now multiple failures I would like to know if we are able to send these cards back for replacement?
Thanks for your responses.

1: reseat card with out cable.
2: cold rest printer/carded installed.
Turn the printer on and allow the printer to start the power-on sequence./

Then press and hold the green checkmark key until all three lights on the control panel are lit.
When Select Language appears on the display, press the Up Arrow key until Cold Reset appears on the display. Press SELECT and the printer will perform a cold reset.

3: try to print a config page.
As you said if there is no link light thne the printer does'nt see the card.

Call in and have then replace, see Serial#
SGXXXXXXX, 800-474-3686...
There is some issues ...

My first guess would be you have a firmware issue taking place on the formatter boards of the printers. Check the firmware datecodes on a few of the printers you find work okay. Of course the compare with those that aren't. Worst part is it is likely the newer date code is the one that is failing. If you are getting nothing not even a test page my first bet would be the formatter itself. At least you have others of the type in house. That sure makes your troubleshooting and elimination processes much easier than most have privy to.