John had to get Quicken 2018 because his version was going to stop working. So he installed it and it's not working. It says it's missing files it needs and it won't let him reinstall it. Leo says that if he installs a backup of his old Quicken data, it could solve the problem. What Leo suggests is fully uninstalling the old program. Then he should reinstall the new program and import his data. A clean install is what's needed here.
Quicken offers an uninstaller called QCleanUI which will uninstall any leftover program files that was left behind from removing the previous version. John should use that first, then start from scratch.