When you launch PSO2, you can probably check task manager and find a service called wsappx forever looping and never actually doing anything but eating your CPU. Well I have a solution to that, basically what happened is that Windows Store is trying to start itself even though it already on. Two things I did that helped.
Start by running the Windows Store Apps troubleshooter.
Open Start > Settings > Update & security > Troubleshoot
Scroll down to the bottom
Click Windows Store Apps
Click Run the troubleshooter
When complete try opening the Store again.
Also check if the Store works in another user account.
Press Windows key + R
Do this a couple times then try launching the Store again.
This all worked for me, hopefully it helps you. I'm gonna go make a sandwich now, gl!