if it used to work recently
try doing a system restore to a time when it did work. If that does not work we can look at the actual causes and solutions but the system restore is a very fast and easy way to fix a lot of problems and it is a logical first step
System restore instructions - windows 7 or 8 or 10
hold the windows logo key down and hit R
type rstrui.exe in the run box that comes up and hit enter
select restore to an earlier date.
Under the "suggested restore" which is usually not old enough to help is a link for "OTHER RESTORE POINTS"
click that if the suggested ones are not BEFORE THE PROBLEM STARTED
choose a date that is BEFORE you experienced the problem
hit ok / restore
the computer will start to shut down
a restoring settngs box will appear with a status bar
when it finishes your computer will restart with the same settings it had on the date you restored to. your data will not be affected.
It is not perfect. But it fixes a lot of things.