No signal on external monitor

I have used Ugreen mini display adaptor (mini DP - HDMI) without any problem, and now there is "no signal" sign on the external monitor. Here are what I tried to do to find the problem.

I connected with other monitor, but the problem remains.

I use other computer to connect the monitor, and it worked very well.

I use friend's MacBook Air to check if there is a problem in the adaptor or HDMI line, but it worked well.

Finally I connected MacBook Air with the monitor with the same line, and boot using bootcamp (Windows), and it worked very well.

So far, I concluded that there is some problem in the Mac OS, so I tried to do some suggestions on the community, (PRAM/NVRAM reset and some other things) but nothing works.

Today I did the latest software update to Mojave 10.14.4, but nothing has changed.

Can somebody help me using the external monitor again?