First of all, make sure that the usage statistics generic plugins is enabled. It comes enabled by default, but it can be disabled by users. Also, if you are not using the server access log files to retrieve statistics from, make sure that your "create log files" setting under the usage statistics settings page is checked. This setting comes enabled by default, but it also can be disabled by managers. If disabled, the plugin will stop logging the access into files.
If you are upgrading your system from a version older than 2.4.3, then make sure you read this: http://pkp.sfu.ca/wiki/index.php?title=PKP_Statistics_Framework#Statistics_migration. In a few words, you're not going to see the same stats numbers you used to before upgrading. Those numbers are still available, but only using the stats reports.
With that in mind, usually, no statistics data indicates that the statistics processing is not working as expected. This might happen for two main reasons:
1 - wrong base_url setting inside your config.inc.php file. Make sure the setting there reflects the exact site base url.
2 - folders permission problems; make sure that the user that runs the php process in your server have access to the usageStats folder inside your ojs files_dir and everything inside of it.
For both cases it should be sent an email notification to your administrator email account to warn you about that. If you have no notification in your admin email, then the stats processing task is not running. For that you can check that you have the Acron Plugin installed and enabled.
To make sure there is no processed stats data, see if there is any file inside the usageStats/archive folder. If there's none, then check the usageStats/reject. If there are files inside the reject folder, then it's probably the error with base_url.
Also, if you can, try querying directly into the database server:
SELECT * FROM metrics WHERE metric_type = "ojs::counter";
This query should return entries if your stats processing is working. If not, check both main reasons described above.
Once you fixed any possible problem, make sure to wait a day to see any numbers in the galley view columns or inside the reports. The stats processing runs once every day.