When i power my RIM BlackBerry Curve 8520 on my screen will not light up but you can read the message on the screen. It reads "App Error 523 RESET" What do I do to get my phone to work?

Just follow the following steps...
What you need...

A PC
Usb cable
Blackberry desktop manager
Blackberry device software(for 8520)
and of course... your phone

First download blackberry desktop software from here.

FOR PC -- DOWNLOAD
FOR MAC -- DOWNLOAD

next download firmware here

DOWNLOAD FIRMWARE
(you may have to enter some details for blackberry newsletter)

after that..

install desktop manager software.
install the firmware..
after installing the firmware go to C:\Program Files\Common Files\Research In Motion\AppLoader and look for vendor.xml and DELETE IT
then,

Open Desktop Manager
connect your phone using your usb cable.
the computer will detect it and install(let it do things)
then just follo the on screen instructions, if it says a backup is needed just click ok, and the software will do the rest.

Just a note though, PLEASE BE PATIENT ON THE PROCESS.
it takes 35 to 45 or even an hour to finish the process. and the desktop manager software might look not responding and the phone looking dead or not responding too. THIS IS NORMAL. just let it sit there and it will prompt you that it is done.

Also be sure to have the batteries have sufficient or full charged(you can charge the phone though it has an error)
If the phone went out during the process, you will have to do it from the start.(except from installing)

Please be sure you also have no other firmware installed for your phone, because the Blackberry desktop software might get confused and install unknown or corrupt files on your phone. If you do have Uninstall it first and install the newer version.