First I would highly recommend exploring options to boot the machine to external media and attempt to copy your important files to an external media device (usb hard drive or such). There are options like "Ultimate Boot CD" or various Linux Distros that may help you make safe your critical data.
The issue sounds like a problem with the windows boot manager files so you could try this
Boot to the install media
Choose repair options
select command prompt
and type
bootrec /fixmbr
and then
bootrec /fixboot
Refer to this article for more details.
How to use the Bootrec.exe tool in the Windows Recovery Environment to troubleshoot and repair startup issues in Windows