I’m not sure that is going to be possible with Ubuntu Mate. Two options I see.
Your external monitor may have a power savings menu you can rely on.
You may be able to search the web and find a script that is designed to suspend a external monitor.
i checked the link no help 
the weird part is if i use unity ubuntu the screen go to sleep normally.
tho the weird behavior of laptop go to sleep when i click restart from menu is the same.
i tried ruining the laptop without mate-power-management on startup
and sleep/turning screen off working but i cant close the lid and have only the external screen ruining.
Ubuntu 17.04 if the newest most cutting edge version of Ubuntu. This naturally leads to the fact that it’s not the most stable version available, because all the bugs have not been worked out yet. I think what you are experiencing is a incompatibility issue between your hardware and 17.04. Given enough time, this issue should be resolved by a future update. The question is whether or not you can live with the problems until the update comes that fixes them.
I looked up the Asus GL502VM, and from what I found online it was released in January of 2017?
If your computer has not been on the market very long, then it may be awhile before everything works with any version of Linux. Sometimes the newest laptops on the market, are not the most Linux compatible.
Sorry for your troubles. Hang in there 
[quote=“steven, post:24, topic:13095”]Sometimes the newest laptops on the market, are not the most Linux compatible.[/quote]First world problems. 
So, if it does work on Unity, maybe this is a feature not yet support in mate-power-manager or mate-screensaver?
thank you all, guess ill wait for now.
hopefully it will be fixed.
my is based on GL502VM but called FX502VM
it was released about a month or 2 before end of 2016
Issue is happening to me, exactly the same. Installed UM today, was sleeping in Ubuntu, not with UM. So since this problem has been going on since 2017, can I assume its not fixed n 22.04? It sleeps when I press the power button, just not automatically as it is configured to do. Sorry for ressurecting the thread. It does sleep if I use the power button, but still does not require a password once woken up. This is kind of a dealbreaker for a laptop. Using the screensaver will lock the computer but won't allow the laptop to sleep.
Hi,
I had some problem like yours on my laptop with UM 20.04.2 about couple months ago.
Also all Power Management settings (at Control Center) were fine but …
I had to go to dconf Editor and change the settings there. It solved the problem.
Please see highlighted path to these settings on the attached image.
Thanks! I will try that
I made the change in dconf. Still not working, however I found a work around: enable blank screen screensaver, active in 15min and lock screen. Then set the power manager to turn screen off after 30 minutes. Seems to work. I will report back. Thanks for the help everyone, you rock!
Only thing here with the workaround is that when the screensaver activates the backlight doesn't go off until the system goes to sleep. As with the Gnome screensaver, MATE screensaver doesn't actually turn the screen off when using the blanking screensaver. But I can live with it.
EDIT: The screensaver activates fine and returning to MATE requires a password, Cool. So that is fine on my desktop as It is set to never sleep. On my laptop, the screen will blank but the system will not go to sleep automatically, I have to choose 'sleep'.
now sometimes on the laptop I have to choose Sleep with the power off menu, the power button doesn't work to sleep even though that's whats configured. And it still wakes up without requiring a password - not secure for a system.
For me, this was solved with a fresh install of UM
