The CAT 5 Ethernet cable network cable is attached to our main Linksys WRT320N DD-WRT router ---> Motorola SB5101U DOCSIS 2.0 Cable Modem ---> Coaxial cable from wall outlet. Another computer is also directly connected to the same router via CAT 5 Ethernet cable and two more computers are wirelessly connected to the same router and none of these three PCs are experiencing issues so this should rule out the router as the culprit.
The issue/symptom/scenario: If I leave the computer on (even for hours) with no network cable attached to the computer, it does not turn off. But as soon as I plug in the network cable, the PC will shut itself off within 5-15min.
Based on the same scenario as described above, here are the troubleshooting attempts I made without success, except for numbers 4 and 6:
1. Switched to different network cable and router port.
2. Disabled Network Adapter connections in "Network adapter settings" for both the onboard ethernet port and wireless adapter.
3. Ran MSCONFIG.EXE and rebooted in diagnostic mode. Only basic Windows services are loaded. No startup programs are loaded.
4. Rebooted in Safe Mode with networking but could not establish any network LAN/WAN connection. Computer did not shut off!
5. Cloned entire hard disk to another hard disk and switched SATA data and power cables on the same computer.
6. Installed fresh Windows on different hard drive on the same computer. Computer did not shut off!
Out of those 6, only numbers 4 and 6 were where the computer remained on and didn't shut off at all after the network cable cable was plugged in.
Cause: What could be the problem?
Solution: How could I fix the problem without re-installing the operating system?
If a fresh install is fine you should probably start checking for the more obvious stuff. You know. Viruses. Spyware. Malware. Things that would connect to the internet to get control. Corrupt drivers causing problems. Hardware wouldn't make much sense to start with