it would depend what the problem is that is keeping it from starting. Do you get any error messages ?
If it worked recently you might want to do a system restore to a time it was working. If that doesnt work we can do some more in depth trouble shooting
System restore instructions - windows 7 8 10
hold the windows logo key and hit R
in the box that appears type
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 from the calendar that is BEFORE you experienced the problem
hit ok / restore
the computer will start to shut down
a restoring settings 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.