This seems to be a weird problem. The exact error is this:
Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 337608 bytes) in ...
It only hangs the dashboard. The other part of website has no problem. The file name where the error happens is different at different time and I can't reproduce the error as I want.
Most probable reason of this error is activating plugin. So, I tried to activate all plugins one by one and the error occurred. I thought that plugin was the culprit. So to work in dashboard, I changed the name of the plugin via FTP and Dashboard was back. Then I renamed the plugin folder to its original name and activated the plugin again to reproduce the error.
But this time it activated without any problem. I tried activating, deactivating other plugins and the same thing happened again with another plugin. After renaming the plugin folder, the error wasn't gone this time. Instead, it showed the error was in
\wp-includes\functions.php and when I reloaded
\wp-includes\theme.php. After I reloaded again, it worked and Dashboard was back.
So, the problem is I can't seem to locate the origin of the problem. Does anyone have any idea?