I upgraded from 15.04 to 15.10 and received some system errors. Reinstalled 15.10 without checking the format box -- so all user files untouched Now receive "end kernel panic not syncing: VFS unable to mount root fs on unknown block(0,0)". There are two other Ubuntu 14.04 on same disk. I am using one of them now. Ran bootinfoscript. Not sure how to interpret RESULTS.txt file from bootinforscript output. Need guidance on what to do. Thank you for your help.
Installing to a partition that has Linux without formatting is never a good idea, there are probably leftover config files from the previous install causing problems. Your best bet is to copy any important files off, reformat, and reinstall Ubuntu.