This sounds like a problem with your deployment/cache.
Try these steps;
- clear/delete the /var/ folder
- clear the cache (magento cache:clean via the CLI)
- run the magento setup:di:compile command via CLI
Edit: I had another similar issue today, where there were no errors of any kind. At last I found permission-related issues in the serverlogs. When I fixed the permissions, all was working again!