Not much in the way of actual information in your post.
How did you arrive at your current situation?
What do you actually see on the screen?
There are any number of software and or hardware issues that can prevent a system from booting.
Do you have backups of your critical data?
Do you have the Windows 10 installation media from which you can boot your system?
If you do not have the installation media on hand you can download the ISO from here
Once you have the ISO, you can use ImgBurn to burn it to a DVD,
http://imgburn.com/ (dual layer burner and media required)
or Rufus to burn it to a USB ThumbDrive,
http://rufus.akeo.ie/ (8 gig more than adequate)
either of which you can use to boot your computer.
When you boot from the installation media you'll see a Repair your computer link on the page following the language and keyboard preference page.
From there you might try
System Restore
Startup Repair
Go Back if available and applicable