Monitor won't stay in standby mode GA-G33M-DS2R

GA-G33M-DS2R with SATA HD, E6750 CPU, on-board graphics, running XP Pro SP2
+ latest updates.

After setting the monitor to 'power off' after 10 minutes, it enters it's
standby mode, but always wakes up again after about 2-3 minutes. I have
unplugged the mouse with no difference. The monitor is set to Plug & Play
type. I have installed the latest BIOS (F7) and on-board VGA drivers from
the web site.

Any ideas please?

Thanks,
Steve