Possible malicious software interfering with ethernet ports

David, This is purely the AVG Support Community. How does your issue tie in with AVG?.
AVG Guru

My desktop's computer Ethernet port keeps jamming and locking up and then after a few keyclicks locks most functions on the computer. This problem started a couple of weeks ago, and occurred maybe half an hour after switching on the computer.  It now appears towards the end of the startup sequence and prevents me from successfully starting the computer with internet access enabled.

 At first I suspected the Ethernet driver or the hardware.  To check if this was the case, I thethered the computer to a mobile phone and used pdanet, with its own driver, to set up a new network connection via a usb port, independent of the motherboard's Ethernet adapter.  This worked for a couple of minutes and then locked up with a yellow triangle displayed on the Ethernet icon.

I have discovered a workaround for the onboard Ethernet but I have not solved the basic problem.  The workaround is: 1. Manually switch off the computer.  2.  Unplug the Ethernet cable and start the computer and wait until all of the startup applications have loaded and the computer goes into idle.  3.  Locate the Ethernet driver and disable it.  4. Plug in the Ethernet cable   5. Locate the Ethernet driver again and enable it.  This causes the Ethernet and internet connection to be re-established.  This is then good for some time but eventually, after maybe half hour or so, the Ethernet locks up again.  Can anybody help?

Thank you.  I have done a scan with AVG antivirus which finds no threats.  There is clearly some software somewhere on my system that interferes with ethernet and also with a tethered network port via usb that gets activated towards the end of the startup process and maybe at other times.  I am trying to rule out malicious software and wondered whether AVG had ever come across viruses or other malicious software that affects internet access.
PS the computer does not have a WiFi adapter.

Hello David,
We are sorry to hear that. There is very less possibility for a Malware to effect your ethernet port. To assist you better, could you please let us know if you have tried to scan your computer completely using AVG? If there was no threat detected, please try to connect to Internet through wireless connection and check if the connection is stable.
Thank you

David, This is purely the AVG Support Community. How does your issue tie in with AVG?.
AVG Guru

Hello David.
Thank you for the information. Please be informed that we have never come across any malware affecting the ethernet port of your computer. This issue can be caused due to different reason, we suggest you to reinstall the network adapter from your computer and check if that fix the issue. If you still have any issue, we suggest you to contact your system manufacturer.
Thank you

Hello David,
You are most welcome. Feel free to contact us for further query regarding AVG.
Thank you