Here are the computer specs of the computer in question: Ultimate SP1 64-bit Xion 600W PSU XON-600F14R-201 Asus M2N32-SLI Deluxe Motheroboard nVIDIA nForce 590 SLI Chipset BIOS Revision 1402 NVIDIA GeForce 8800 GTS 640MB AMD Athlon 64 X2 Dual Core 6000+ 3.15 (15 x 210 FSB) Muskin 4GB (2 x 2GB) 991587 DDR2-800 SDRAM 5-4-4-12 Koolance EXOS2 Watercooled OS Drive: Seagate Barracuda ST3500820AS 500GB DATA Drive: Samsung HD501LJ NVIDIA nForce 10/100/1000 Mpbs Ethernet Realtek RTL8187 Wireless 802.11b/g 54Mpbs USB 2.0 Network Adapter 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?