you may have tried the first option here before. if it isnt working go to the next etc.
If you can get the windows 10 desktop
right click on the start button
and select SETTINGS
then accounts and recovery
that should give you repair options you can try
if you cant get anywhere on the desktop but you can get to the sign in screen
at the sign in screen before you log in
there should be a button to restart the computer on the right hand side
if you hold the shift key on the keyboard down while selecting the restart option
it should bring you to a page with some repair options that you can try.
if you can not get the computer to do anything useful at all than you need a boot disk ( actually a flash drive)
you can create the flash drive using the program that you download from this page
make sure that you select the option to create a flash drive for use on other machines
you can put that flash drive in the computer and restart it and it should reboot from the flash drive that will give you some repair options you can try including going back to your
original operating system or re installing the windows 10 totally