Hello and welcome to the forum.
Sounds like you're going to need a copy of the installation media. You can download the latest Windows 10 ISO here
https://www.microsoft.com/en-us/software-download/windows10
Once you have downloaded the ISO you can use ImgBurn to burn it to a DVD
http://imgburn.com/index.php?act=download
OR
Rufus to burn it to a USB ThumbDrive
http://rufus.akeo.ie/
When you've created the installation media then you simply launch setup.exe from the media from within your current version of Windows to perform the in-place upgrade, OR.....
perform a custom clean install, OR....
Boot the computer to access the Windows Recovery Environment to use some of the advanced troubleshooting tools.
When you've managed to boot from the installation media you need to click the Repair Your PC link on the second page after the Choose a Language and Keyboard layout page.
That should get you to the Advanced Troubleshooting options.
From there you can use Startup Repair, System Restore or even Starup Settings to attempt to boot the system into Safe Mode to see if any of those options help with your issue.