If this happened "out of the blue", (ie: was working and then suddenly isn't) then there are numerous things to check ... because obviously "something" changed.

Between the time when things were "working", and now they're "not" ...
- what software updates has the hosting company installed on the server?
- did they change PHP versions? Apache version? These could have changed default configuration settings in php.ini
- who has had access to your server's control panel?
- have they made any changes to anything, especially PHP/Apache settings?
- who has had FTP or filesystem access to your server?
- have the uploaded/edited anything? Are you sure?

Have you been making regular backups of your server's files and your store database?

It's worth taking a copy of your server's current files and database, and comparing them against a backup from before the problem happened. This can help identify unexpected/unauthorized changes. In short, it's worth proving nothing's been tampered with, by going through these steps until you've verified that nothing unauthorized has happened: https://www.zen-cart.com/wiki/index....ing_From_Hacks