Wordpress Stop Responding Randomly with unclick able webpage

Hi,
I have weird problem with my multisite wordpress. This happen across all sites so i think this might be problem with the main site.
When I click update or click on any link on the admin section, usually what happen is WP will load the page. But in my case, during the load, it will stop responding. The loading progress bar on my chrome will stop and everything on the page is unclickable. My solution is just to press refresh. It might take one refresh or multiple refresh just to get it back. Usually any update I make will be updated after i click on the refresh. Its like during the loading progress, WP stop responding or being terminated. What happen?