Network Adapter issue

Hi All

I'm having a unique issue with my Lenovo A70z All-in-one machine. Its a windows 7 32-bit sytem. A few weeks ago, one of the users reported that their machine stopped working. I checked and the internet icon had an exclamation mark on it. I tried few things but it didnt help. So I brought it to my office and started troubleshooting it.

First thought was that it is a hardware failure so I tried Cisco USB 300 Usb to ethernet adapter, assigned it an IP (we only use static IP's) and tested it but it didn't help. Same exclamation mark. At this time, it was connected to a small trendnet switch where my personal laptop is also connected. So a trendnet switch where wall cable plugs into and then two cables connected to the switch (one my laptop and other is this Lenovo machine). I noticed that after few minutes my internet connection showed an exclamation mark. I disconnected the wall cable from the switch and plugged into my machine and my internet started working. I then ran all sorts of virus detectors, malwarebytes, TDSSkiller, Combofix and few other but nothing popped up.
I then tried to connect the wall cable directly to affected machine and still the same issue with yellow exclamation mark. Sometimes I noticed that ethernet adapter manual settings had gateway address missing so I entered it again (even though I'm 100% that I entered it the first time).

So long story short, I'm still having issues with the machine. I installed fresh windows 7 32-bit (deleted the system and C: partition and then recreated the partition), didn't touch the recovery partition and after fresh install, i was still having the same issue. I then fdisk the machine removing the recovery partition and started fresh. The built-in ethernet adapter still didn't work but the USB -ethernet adapter worked for 30 minutes before giving up. I posted this in malware section thinking it could be a malware issue but one suggestion i got was "Possibly broken hardware due to a power surge or some other failure. Sometimes this could impact other ports in a PC too. You would be better off trying to address this non-malware topic in the Hardware or possibly Networking Forums". As an IT person, I'm interested to know what would cause the issue. Any help from you guys would be greatly appreciated. I also updated the nic drivers but that didnt help.

Any help is appreciated