Boot the problem PC from the installation media
The installation media can be obtained through this resource.
https://www.microsoft.com/en-us/sof...459594)(TnL5HPStwNw-WaTVja5C7z2Vs7q82apCPg)()
It's very important that you match the ISO download to the appropriate system architecture.
Once you have the ISO, you can use ImgBurn to burn it to a DVD or Rufus to burn it to a USB ThumbDrive, either of which you can use to boot your computer.
http://imgburn.com/index.php?act=download
http://rufus.akeo.ie/
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 Troubleshooting -> Advanced Troubleshooting
Try performing a Startup Repair.
My wife has a Dell Inspiron with Win7. She downloaded W10 and started the installation
NOTE: It's a bit late in the game to take advantage of the "free" upgrade (excepting for certain specific circumstances), so .....
Upgrading from Windows 7 to Windows 10 now, may have a cost associated with it.