"it happens after reboot without a mouse plugged in"... i don't think an optical mouse would cause this problem... i've heard of this happening with a shorted ps2 connector... doesn't matter if your using usb or if anything is plugged in or not... the ps2 is still shorting and causing the mouse to move... i would go into control panel.. then system... then device manager... then go to input devices... then click on ps2 mouse... or whatever it says... you know.. then disable it... hook up a usb mouse and restart the computer... see what's movin!