reset video card to factory setting, reboot if it still goes to sleep,remove added on video card hook monitore up to onboard vid card
More aboutmonitor sleep mode instantly
I had two like that with - Viewsonic both times and I found that capacitors died. It posted through BIOS and it turned to sleep. If the power button was pressed on /off it did go on for few seconds and back to sleep.
Does it sound like your issue?
I had that problem, also with Viewsonic. I'm looking fora repair at the moment so I hope it's justa few capacitors as it's one of a matched pair.