Is your new Soyo SY-KT600 mainboard replacing another SY-KT600 mainboard, or is it an upgrade from another brand/model?
If its the former, did you upgrade the CPU at the same time? Windows XP Activation sometimes gets upset when you change CPU models, and it doesn't always give you a 30-day reactivation grace period.
If its the latter, did you reinstall XP? Remember that when you switch mainboards, you're introducing a complely new set of devices which needs a new set of drivers. The largest show stopper is the mass storage (ie, EIDE, SATA, SCSI) controller driver. Unlike Windows 95 and 98 which can fall back to 16-bit BIOS compatability mode for these devices, Windows NT based operating systems need the driver installed and configured. If you don't, you'll see a blue screen warning about an "Inacessable Boot Device" failure.
There are two ways to get around this problem. First, before ripping your drives and such out of your old system, drop in a Windows XP installation disc and perform an "upgrade". After it copies the setup files to your hard drive and reboots, power down and swap in the new mainboard and such. When you power up, the XP setup files are already loaded on the drive. Setup will load every driver there is and then proceed to reinstall.
Another way to do it I hear is to autoboot off the XP installation CD and perform a "repair" of the system. I can't say how well this works, but I assume it would be faster, and would not require a reapply of all XP service packs and hotfixes you've installed.