Sorry the long time to reply, I just saw your question inside your last message today.
In the plugin management page, inside the generic plugins category, find the acron plugin and please make sure it is enabled. Also, make sure you click on the "reload scheduled tasks" action.
Also, pay attention to the time period you are using to generate the custom reports. You must have usage stats for that period to see something in the report.
If you follow those recommendations and still can't see any data, check if you have files inside your ojs files folder, under usageStats/processed folder. If you have not, please make sure with you system admin that the user that runs php have access read and write access to the ojs files folder, specially the usageStats and below.
The process to read the log files and grab statistics from it runs once every day. So, after you check what I said above, wait for one more day and check again the reports. If you can't find any data still, let us know.