Monitor will not turn on with pc, or when resuming from standby unless I cycle power

Like the title says, my junk computer, the one I built from spares for a friend will not send the wake up call to any monitor, I must cycle power on the monitor to wake it up.

Motherboard: Abit BG7 using the onboard 845G video
Ram: 512MB DDR 2700
CPU: Celeron 2.4
PSU: I am using my 24pin Antec Neo HE 500 on a 20pin mobo to test the board - could this be the problem? I’ll go check.

Everything else seems to work fine, any ideas?

I doubt the power supply is the issue.

Does he have suspend or hibernate enabled?