E-Machinist talked about AT era pcs needing to be shut down by pushing in the power button. Actually, i have a pc right now that has a slot 1 P3 933 cpu in it, and i do believe the mobo might take a faster P3 cpu and this unit is still shut off using the "push in the power button" method. Its also running win xp pro.
So its not just old ATmachines, although i agree this is still old stuff and with
vegasgmc's pc sporting a 2.6 mhz cpu then its not likely that this is the issue.
I think, as some have stated, there could be a problem with the mobo, but i also think it could be that there is possibly a setting in the bios that might control this. I am wondering if its not even a combo of certain hardware in this system and windows itself doing this? This is just a guess and i dont know what hardware could cause or promote this.
It couldnt hurt to even try to install your os over top of itself, just a suggestion.