Replaced a failed mobo with DG41CN mobo, E5400 CPU, and 2gb Kinston PC-6400 RAM. This is a single HDD system. Performed a repair install of Windows XP Pro. Sounds simple enough, but I've built and rebuilt it 8-10 times, each time changing out different components, with the same result - Cannot log on after installing windows or Windows XP Pro will not install at all. Early on received 1 beep every 15 seconds (Refresh error) and Windows XP Pro refused to install. Found the Refresh Error tied to Core Multiplexing Technology setting in BIOS - Disabled the Core Multiplexing setting and Windows XP installed. However, with the Core Multiplexing setting still disabled, the Microsoft authentication window appears requesting re-authentication within 3 days. Cannot bypass this with either the Yes or the No answer. Each answer bring Windows XP Pro back to the log-in screen (remember this is a repair install so the users is already setup with a user name and password). Went through the same excersie with a new hard drive. Same results as you read previously. Not only was the HDD changed out, but so was the power supply, the DVDROM, the RAM, the CPU, the MOBO, All changes resulted with the same outcome you read earlier. Updated the BIOS. Same issue. Same outcome. With the Core Multiplexing setting Enabled Windows just keeps beeping and restarting. Very frustrating.