Why aren't my apps working since upgrading to Denim?

[Windows Central Question]

Issues after upgrading to Denim

I use a Lumia 925 and was having Lumia Cyan installed. Yesterday I got a message informing an update so I clicked OK. Lumia Denim update was downloaded and installed without an issue but it was very disappointing to note that some of my very important apps are not working. Calendar, Files, Battery Saver, Foursquare, Podcasts, Shazam, Bing Translator. The apps appear faded and cannot click. The message indicates installing (From yesterday) I tried uninstalling and installing the foursquare app but cannot install and it gives a 800b0109 error. Please help

 

[N_LaRUE]

Re: Issues after upgrading to Denim

Doing a quick search it would seem that error indicates a corrupt update.

It looks like you're going to need to use this - FAQ - How can I recover/reset/restore my phone software? - Microsoft - USA

You'll need a PC and the internet. Make sure you back up what you can. This wipes your phone clean and installs a new firmware.