I had the same issue when I upgraded to 8.1 where the Store and music app would not open. The issue was related to the time/time zone being off. Once I corrected the time zone I was able to get into both apps.
rusher
One feature I'd like to see in the Mail app is the ability to view all inbox's on one tab similar to the email app on an IOS device. I have multiple mailboxes and it is a pain to have to click through each to view emails as they come in.
Bill
My SP seems to run hotter as well on battery. Do the fans normally run only when on power cord? I noticed once that the fans stopped running when I went to battery, but it could be coincidence.
Bill