I am unable to install or update metro apps through Windows Store after upgrading my system to Windows 10. The new OS is more or less useless for me this way.
The problem arises due to the excessive cache files that clutter-up your system, causing various issues including this one. This problem could be solved by cleaning those cached files, which can be done using these steps:
Press Win+R keys to open the Run dialog
Type “WSReset.exe” and click OK
A blank, black window will appear that will auto-close after sometime
Windows Store will also open thereafter, and even if not, open Windows Store yourself and try installing or updating apps now – it will work