Ethernet cable overheating

Standard 100 base ethernet only uses two pairs so this works... what is a little worrisome is it appears someone did it on the cheap and saved a couple of cents by omitting the other pairs. That said, 1000 base ethernet may use all four pairs and this cable can't handle that.

You need to narrow down the problem. Firstly try booting your pc from a "live cd". My personal preference is an Ubuntu image loaded onto a usb stick but you can also burn and boot from a DVD.

If your router-cable-pc then connects to the internet with no issues, you can rule out hardware and attempt to diagnose problems within windows. My suggestion would be some or all of the following:

1. Disable or remove software that might interfere with your connection. eg firewalls, anti-virus or other internet security software, connection managers.
2. Scan for malware or viruses.
3. Delete the network card from the device manager and then reinstall the card and drivers, perhaps trying once with the Windows default drivers and then again with the manufacturers drivers.
4. System restore might also help you get your pc to a working state.

If the live cd also shows problems, then it suggests a problem with the hardware but the symptoms could also be due to a problem with drivers or support of the card. Check via google to see if your card is fully supported. Ubuntu can be downloaded from http://www.ubuntu.com/download/desktop