If everything was working fine but now is not and you have not changed anything yourself, then it sounds like something may have changed on your web server which is causing the problem.
Please check in with your web host to see if they have made any changes to your hosting account recently (e.g. change of PHP version, migration to a different web server, etc.) which might somehow be contributing to the problem. This might give us a clue to the nature of the problem and point us in the right direction.
If you have not already done so, then try running the Showkase setup (in case your web host has moved your site to a different web server).
If running the Showkase setup does not help, then perhaps upgrading Showkase will help.
If you are not already running the latest version of Showkase (v1.7.6), then please try upgrading to see if this helps.
Showkase is kept up-to-date to be compatible with the latest versions of PHP and, but if you are currently using an older version of Showkase and your web host has upgraded the version of PHP on your hosting account, then this might be the cause of the problem and upgrading Showkase may help.
You can find full instructions for downloading the latest version of Showkase and upgrading on the Upgrading Showkase support page.
Even if you are already using the latest version of Showkase (v1.7.6), try going through the upgrade process but with the v1.7.6 files. If there are any missing or corrupt source files within your Showkase site, going through the upgrade process will reinstate them with fresh versions. (Make sure that your FTP program is set to overwrite existing files.)
When upgrading your Showkase site, please be sure to make a complete backup of your existing site first, just in case anything should go wrong and you need to reinstate your original files at a later date. You should not encounter any problems upgrading Showkase but it would be wise to have a backup of your site should anything unexpected happen. Also, if you have made manual customizations to any Showkase source files (or to your theme's custom.css or custom.js files), then please note that they may be overwritten when you upgrade and you'll need a backup in order to reinstate them afterwards.
Please let me know how you get on and if I can be of any further assistance.