there can many reason of this issue but mostly it happens because of slow computer freezing or dust inside the computer . use a air blower and clean the computer while its turn off and remove some of programs which is using lot of your processors power and memory . try updating the computer it also helped many people in this problem . try cleaning some software and clean computer use this post 10 ways to make your computer faster and see if this also helps you .
only thing i can think of is restart and unplug for 10 min . because this can be easy fix with right steps follow all the steps mention in this article Fix-Laptop is not connecting with TV using HDMI Port and i hope this will get you the help and fix the issue .