I am running my website for moe tha 2 years now and never faced this kind of issue, however, I faced this problem only twice in last 7 days.
When I open my website (http://registerkbc67.com), my website is redirected to the wordpres install.php page and shows the same options to install the wordpress as it was never installed. When I deleted the install.php from installation directory, then my website started showing some page not found errors.So I had to re-upload the install.php. This issue remains about 4-5 minutes and goes off automatically and then everythings work as normal and fine.
I just know how to use WordPress and have no idea where can I start to troubleshoot this issue. I am not getting even a valid logical reason why this issue occurs and goes off in few minutes automatically. Please help me! I fear if somebody, while seeing the install.php options on the page installed the WordPress again, it will be worst for me.