After update to 10.13.1 iMac constantly goes to sleep

Upgraded my 27 iMac to High Sierra and everything was normal.

After updating to latest version 10.13.1, my iMac display constantly goes to sleep even when energy settings were set to never for both hard drive and display. Sometimes it will wake for only a few seconds when either keyboard space bar or power button is pressed. Have tried reset SMC & NVRAM and problem still persist. Unable go into safe mode as screen seems to be stuck with no response even when progression bar is fully completed.

Appreciate some expertise advise as to how I can resolve this issue.