Error on my website

Try:

– deactivating ALL plugins temporarily to see if this resolves the problem (plugin functions can interfere). If this works, re-activate them individually (one-by-one) to find the problematic plugin(s). When you can’t get into your admin dashboard, try deactivating via FTP or SFTP or whatever file management application provided by your hosting provider (cPanel…). Also remember to deactivate any plugins in the mu-plugins folder (If you have created such folder). The easiest way is to rename that folder to mu-plugins-old.
– If that does not resolve the issue, try switching to the unedited default Twenty Fifteen theme for a moment using the WP dashboard to rule out any theme-specific issue (theme functions can interfere like plugins). When you don’t have access to your admin area, use FTP or SFTP or whatever file management application your host provides. Navigate to /wp-content/themes/ and switch to the default theme by renaming your current theme’s folder by adding “-old” to the end of the folder name. Alternately, you can remove other themes except the default theme. That will force your site to use it.