I know this has probably been answered many times before, so please send me links if you know.
I had Ubuntu 16.04 (three years ago), added Windows 7 (two years ago). Setting it up was very hard, but I did it successfully (Ubuntu on hda1, Win 7 on hda2).
Last month, I had a failure loading Ubuntu, but Windows could launch using a Boot CD and Boot Manager (pointed to hda2). Last night I reinstalled Ubuntu (18.04) from a Live DVD in the original partition. BUT Now Windows cannot load, either from GRUB (it is listed there) or from one of those Boot Managers that point to hda2. Instead, I get a complicated series of error messages from grub (recalculating checksums, advice to run "bootsect /nt60 SYS /force", others).
Can this be easily fixed?