Ok, I have an 8150N that stopped working. It prints config pages just fine so it isn't the 'printer' per se.
I have two others so I have switched out parts and eliminated the JetDirect card itself. I tried another EIO unit (has 3 eio slots in it) and that didn't do anything.
The link lights won't light up and the config page shows EIO 1, 2, and 3 are not there. The same Jet Direct card and cable work fine on another machine.
What would be bad? Maybe whatever the EIO unit slides into? I have checked the connection and feel a positive connection when I slide it in.... so I'm convince it is seated.