internal server error

when i click on user management from back end, i am taken to a page with error "internal server error"
this also happens on clicking any link to user management, list management and new list
I have re installed CB but no change
I uninstalled, and re-installed no difference
I uninstalled, deleted all CB tables in database and re-installed also no difference.
Please, anyone have an idea what the problem may be?

Enable debug mode and maximum error reporting in Joomla global configuration then retry to expose any errors. If nothing check server error log.

Thanks for your reply,
I Omitted to mention that I also enabled debug mode in Joomla no errors were shown except the "500 Internal server error"
I have now enabled maximum error reporting, also no errors were shown except the "500 Internal server error"
I checked the server logs, no errors in php
but in main server log i have this error
"Fri Oct 13 08:43:45 2017] [error] [client 41.58.99.185] Premature end of script headers: index.php, referer: http://xxxxxx/administrator/index.php?option=com_comprofiler&view=showLists&cbprevstate=b3B0aW9uPWNvbV9jb21wcm9maWxlciZ2aWV3PWVkaXRQbHVnaW4%3D"
thanks

I should mention that it is possible to view the memberlist from front end

With Joomla debug mode and maximum error reporting enabled you should see the server error. It's important both settings are set. If nothing is output the error should be in your server error logs. Your error is a server error. So PHP or SQL is erroring.

As you mentioned, both Joomla debug mode and maximum error reporting are enabled.
I checked PHP logs but there were no errors

but in main server log i have only this error:-

"Fri Oct 13 08:43:45 2017] [error] [client 41.58.99.xxxx] Premature end of script headers: index.php, referer: http://xxxxxx/administrator/index.php?option=com_comprofiler&view=showLists&cbprevstate=b3B0aW9uPWNvbV9jb21wcm9maWxlciZ2aWV3PWVkaXRQbHVnaW4%3D"