Honestly it sounds like a bad Mainboard. Soyo makes junk. Buy ASUS. Your computer should not lockup, especially in XP.
To make sure do the following:
1. Update your Bios K7VXA_2BA4 (
http://www.soyousa.com/downloads/filedesc.php?id=1920)
Load Optimized or Setup Defaults, save and exit.
2. Run Memtest86 v3.0 (
http://www.majorgeeks.com/article.php?sid=1247&cat=26) to make sure your memory is ok.
3. Run Datalifeguard v10.0 (Win9x, ME, 2000, XP) (
http://support.wdc.com/download/dlg/dlginstall_10_0.exe) on both HDs to make sure they are ok.
4. Go into Safe Mode, start run, type msconfig, startup tab, disable all startup programs.
5. If you do get into Windows run a Virus Scan Trend Micro Housecall (
http://housecall.trendmicro.com/housecall/start_corp.asp).
6. Run Windows Update till nothing is left, expecially install SP1 for XP, this fixes alot of those Stop error messages. Also install IE v6.0 SP1.
7. VIA 4-in-1 Chipset Drivers v4.43 (
http://downloads.viaarena.com/drivers/4in1/VIA_4in1_443v.zip)
8. Nvidia Drivers v40.72 (Win2000, XP) (
http://www.nvidia.com/view.asp?IO=winxp-2k_40.72)
If none of that solves the problem you could very well have a defective mainboard.