I just happen today.. I have no idea what happen or what cause it I had unplug and plug it again the hdmi cable...
what it look like: https://cdn.discordapp.com/attachments/348391495902035969/693054858009378848/image0.jpg
My monitor: Acer VG240Y
Cpu: Ryzen 5 2600
Gpu: Gtx 1070
what it look like: https://cdn.discordapp.com/attachments/348391495902035969/693054858009378848/image0.jpg
My monitor: Acer VG240Y
Cpu: Ryzen 5 2600
Gpu: Gtx 1070