HP MEDIA CENTRE m1190.uk Monitor Power Saving Problem

My HP Media Centre has started putting my monitor into power save mode (switches screen off) about 60 seconds after startup. It does this before windows actually boots up. I have replaced the video card (ATI X600 Pro) thinking it was the problem but the problem persists despite this. I have reset the BIOS to default settings again to no avail. I have tried switching monitors to another flat screen and a CRT monitor all of which has no impact. I have used the reset bios function on the motherboard again to no avail. Does anyone know what is causing this fault and how to rectify it?

Thanks

Craig