I can make phone calls just fine but when I play videos, there is no sound. I have checked everything I can think of to check.
Did you use the built-in video player? If you haven't done this, try playing videos using a third party app from Play Store, and if it is still getting the same result, sadly you're gonna have to start over and normally by doing factory reset will do the trick on android stock roms -- if you said you've done everything you could to fix it, but the result is still the same, well this is the last thing to do. but if you're using a custom rom this is another story and perhaps may even lead to be some sort of a bug.
There are 4 types of volume levels.
When you press, volume down or up, volume slider will appear , press gear icon then check whether your "
media" volume is set to be zero or not.
If this does not work, try to restart.
Hope this helps