410,
Has any of the hardware you listed in the PC spec been recently added/changed ?
I suspect a hardware/driver conflict. No expert on XP but my inklings lead me to that.
Do you know what BIOS version you are running ?
It's a simple procedure to reflash the BIOS if there is a later version.
From your posting, seems like the PC boots OK and this occurs during normal use ?
Certainly worth a BIOS reset if you are confident to open the case and either move a jumper over or remove the MB battery.
Just filling in (rather badly) until Richard logs on !