Do you have the user manual?
If not, here is a link via LG:
http
/www.lg.com/uk/support-product/lg-49UF770V#
See page 19 regarding automatic standby. Hopefully that information will help.
Did not note any reference to a power LED.
In case I have not found the correct manual/guide just search LG for the correct manual/guide.
If the automatic timer etc. is not the problem, then I suggest that you "chat" with a service representative and let them walk you through some additional, if any, troubleshooting.