External monitor - flickering screen - Asus pg278q

Hi,

I am using model MacBookPro11,2 (Intel Iris Pro) with an external monitor Asus pg278q. Each time i close the lid to use the external monitor i get this flickering screen. When i close the lid, the refresh rate on the monitor changes from 60Hz to 144Hz. I had the same problem in OS X 10.11 and now in 10.12. I have connected the monitor with a DisplayPort to miniDisplayPort cable. Normally, i keep the lid open and brightness to zero and work on the monitor.

I have tried to reset NVRAM but no improvement. I couldn't do SMC reset. The magsafe connector did not change its color upon reseting SMC. I followed the exact instructions on resetting SMC given from Apple.

I am looking forward for your suggestions. Thank you!

Mst