I got a Question regarding video playback

ok ive got a computer that ive built its a decnt rig, im running 1.25 gigs of ram windows xp p4 cpu, 256mb agp card and a asus motherboard. I reccently wiped everything off and put windows xp pro back on. Ive got virus scanners and spyware scanners up the wazoo.... For some reason just reccently whenever i go to play a movie my whole system will hang and my cpu usage goes up to a 100 %. Only thing i can do is close it down by crtl alt deleteing and then itll resume running regularly. I can do anything else perfectly just videos. Unfortunatly reformatting or sytem restoring isnt a option any ideas as to whats causing this? Ive treid using WMP, VLC, GOB, DIVX, REAL,WMP clasic all theese players do it