Try this
Reset your RT from within Windows. Reset, not refresh. Connect the RT to charge.
One of the pages will ask for a drive encryption key. Go to the bottom of the page and select ‘Not this Drive”
When the reset finishes, in settings go to ‘Power and Sleep’, ‘When plugged in’ set to ‘Never’
All updating is done from the Control Panel, Windows Update.
After each search for updates is complete click on the blue line that says ‘important updates are available’ to see what is found. You can speed things up by hiding all Office updates. Right click an Office update and select ‘Hide’. Install all other updates found.
When Windows updates are all done and Update 3 is installed go back and restore hidden updates and install the Office Updates.
Start Update Instillation Here
Turn on WiFi, Search for updates from the Control Panel, you will see a firmware update, install all Windows updates, restart
When you go back to Windows Update it will show updates are available. Do not install these updates. What you need is KB2919355 and it will not be there. Stay on the page and search for updates.
Install KB2919355 along with the other updates. Restart.
Go to Control Panel, Programs and Features, View installed updates. See that KB2919355 is installed.
Turn off Wifi, install KB3173424, restart
Install KB3172614, restart
Turn on Wifi, search for updates, should find over 200 updates, install, restart
Turn off Wi-Fi and install KB3097667
After the restart, right-click on Taskbar > Properties, Start Menu. Check the box, Use the Start Menu instead of the Start Screen for no more metro screen.
finish installing updates
The Microsoft image that is available to download is the same as the recovery partition on the RT if you have ever had 8.1 installed. The recovery partition never changes after you have 8.1 installed.
KB3173424, KB3172614 and KB3097667 are standalone MSI update installer files that you download to install at the correct time.
Download KB3173424 HERE.
Download KB3172614 HERE.
Download KB3097667 Windows RT 8.1 Update 3 Standalone Package