why can't i open my App Store on my MacBook Pro (2011)

Safe Boot from the HD, (holding Shift key down at startup), does the problem occur in Safe Mode?

Safe mode attempts to repair Disks & clears lots of caches, so if Safe Mode works try again in regular boot.

To find out if it's system wide or user specific, try this...

Open System Preferences>Users & Groups, unlock the lock, click on the little plus icon, make a new admin account, log out & into the new account.

Does it work in the new account?

Let’s see if there’s a locked file interfering in the original account.

Open Terminal & paste this command in & prefs enter, it’ll ask for an admin password & not echo what you type, wait for it to finish which will be an empty prompt unless it prints out some locked files, or Operation not permitted…

cd /;sudo find . -type f -flags +uchg

Any luck yet?

can't open app store on mac book pro. added new user and it works