What is actually making the error of ‘403 Forbidden Error’ and makes the WordPress keeps redirecting to wp-admin/install.php?
Your problem is that your WP database is BROKEN!
How to solve it?
1. Login to your cPanel
2. Find the phpMyAdmin and click it
3. Choose the WP database on the left sidebar. (usually named as _wrdp1)
4. ‘Check All’ the table on the page
5. Click on the ‘Repair Table’ (see below).
6. Wait for few minutes (or hours!) before everything is backed up and repaired. I suggest you to install database backup plugin after everything is being repaired.
Thanks!