1
Click your Start button, then just type cmd and on the resulting list, right click command Prompt and select 'Run as Administrator'.
Run this command in Command Prompt and press Enter.
wsreset -i
When that command completes, close Command Prompt.
Restart (not shut down) your PC and check if the Store is working correctly.
2
If not, open the Settings App.
Go to System - Recovery.
Click the 'Reinstall Now' button in the 'Fix problems with Windows Updates' section, then wait for that process to complete.