screen go for sleep mode

You are not saying in what circumstances the screen (or your mac) goes to sleep.

If it happens while you are working on it, it could be that you have set a "hot corner": then if you accidentally move the cursor to that hot corner your mac may go to sleep.

Go to System Preferences->Mission Control, click on Hot Corners and turn off any that you don't want.

Hey there, CaptSalahuddin!

Thanks so much for using Apple Support Communities.

Have you tried pressing a button on the keyboard or the mouse? If that doesn't wake it up, you can also try pressing the power button once and wait to see if the screen powers on.

If none of those steps are working, you may want to try and reboot the computer: Log out, sleep, wake, restart, or shut down your Mac

Finally, if all else fails, we'd recommend booting into Recovery and reinstalling macOS from there. Here's how: How to reinstall macOS

We hope that this information is helpful.

​Have a great day!

As per @ Luis S advise and Find an Apple Authorized Service Provider and find one near to your location

I think you should have your mac looked at.

If the screen turns off or gets so dark that it almost unreadable when you open the lid over a certain angle I suspect that there may be an issue with the connection between the motherboard and the screen. Hopefully this should be a relatively easy fix but it must be done by an authorized facility.