Onboard ethernet port randomly shuts off

If the port randomly quits working, it could be either a hardware issue (defective ethernet controller) or a problem with the OS's stack. I'd try a USB or other add-on ethernet controller and see if the problem goes away with the new card. If it *does* go away, i'd start looking at a possible hardware issue. Why it takes your "shop" weeks at a time to diagnose this is beyond me. Maybe an hour, tops.

Thank you, mavroxur, your analysis makes sense now that I hear it. As to why it takes them a week is beyond me also. I'll give them the benefit of the doubt, the techs may be busy with other repairs, mine just waiting its turn in line. But my machine has always been in their shop at least a week each time I take one box or another to them for the last six-seven years.

Thank you again for your input and analysis.