Install Linux Reader (free). Look for your log files and see if you can fix any errors that show up by editing your config.
Otherwise, using Linux Reader, copy off your latest snapshot, or if you don’t have one, your entire /config folder including the hidden .storage folder.
Reinstall then restore your snapshot, or copy over your config file. You will have to reinstall and set up any addons you use if using the copy method.
In future use one of these to automatically back up your installation off the SD card:
To a NAS: Samba Backup: Create and store snapshots on a Samba share
To Goggle Drive: Add-on: Home Assistant Google Drive Backup
To DropBox: Hass.io Add-on: Upload hassio snapshots to Dropbox
To NextCloud or S3: [New Addon] Snap-Shipper - Webdav and S3 backups (and probably other ways to later on)