First of all, clear the Store cache by opening a Run window (Windows Logo key+R), typing wsreset and pressing Enter.
If it doesn't cure it, check the internet connection, i.e. press the Windows Logo key+X (or right-click or press and hold off the bottom left corner) and choose Control Panel > Small Icons > Internet Options > Connections Tab > LAN Settings (at the bottom) and remove the tick from Proxy server > OK, etc.