Without a Windows disk you are not likely to fix the system as it would need a clean Windows setup and possibly a new hard drive. A lot of issues with starting Windows ends up being a failing hard drive. If you are using Windows 7, you can download the base Windows 7 disks here
https
/www.heidoc.net/joomla/technology-science/microsoft/67-microsoft-windows-iso-download-tool for the version you are running and use the code on the laptop to activate it. You will need to install the drivers from Acer support site for some things like audio and video and possibly the network cards. I suggest you replace the hard drive (with a solid state if possible), run the Windows 7 setup and copy your files over from the original drive if it's still working properly using an external enclosure.