Advice 1
If you see the interface is frozen or looks oddly, but there are no error messages on the screen, then check the browser console for error reports.
Advice 2
If you see just a blank (empty) screen then it could be either a javascript error or a server error.
- To detect a javascript error please follow the Advice 1.
- To detect a server error please follow the Advice 3.
Advice 3
Set the proper error reporting for your PHP interpreter:
- enable
display_errorsPHP option - set the
error_reportingto a high level (I recommendE_ALL | E_STRICT).
Advice 4
Switch Magento 2 to the developer mode.
Advice 5
See Magento error reports in the var/log folder.
Generally, you can see 2 files there: system.log and exception.log.
system.log usually contains a lot of low-level information and I do not think a generic administrator is able to properly analyse it.
So I recommend to see the exception.log only.
Advice 6
If Magento 2 runs in the production mode (not developer mode) then it does not show the actual error message on the screen, but shows a generic message: There has been an error processing your request and creates a detailed error report in the var/reports folder. You can find the error report file there by its report ID which is shown on the screen.