Did you break something and do not have access to a backup of your files and database? It does not have to be a worse case scenario. But it might require a little work. Here are steps you might find useful in recovering from a complete meltdown.
Note: All PHP errors are logged in logs/errors.log. See if you can resolve the issues by investigating any erros listed in the log. Otherwise continue with the following steps:
1. Replace your installed platform with a fresh new set of files.
2. Copy the following files and directories from your broken platform:
3. Disable any copied vqmods in the vqmod/xml/ folder by renaming their filename extension from .xml to .disabled.
4. Compare your database structure with a fresh installation. You can use phpMyAdmin or the Litecart add-on sqlBuddy to export the database structure (not the data). Compare the files with a file comparison software e.g. WinMerge or DiffMerge. Make sure your database structure conforms to the fresh new structure by correcting any inconsistencies.
5. Make sure the database entry lc_settings → key:platform_version is set to the same version number as your fresh new set of files.
6. If you still are having issues, investigate the recent upgrade patches to see if any database data in the database tables should be transitioned.
7. Go to Admin → vQmods and enable your vqmods one by one to see if they function properly or not. If they don't, see if there is an update of the add-ons or visit the support forum for the add-on.