Welcome to the BBForums.
Make sure you have Desktop Manager installed, you said you did. Should be at least version 4.2, with Service Pack 2, the roxio media software is not required.
Get your OS downloaded. The latest for the 8703 is this: http://www.blackberryforums.com/gene...-106-cdma.html
You can follow those instructions at that link.
Reboot the PC from start. Run Desktop Manager, now, and see if it connects to the BB. Run App Loader and install theh OS.
If none of that works, you will need to wipe the BB like this, and load the OS, again. How do I wipe the BlackBerry using Jl Cmder? - BlackBerryFAQ
It will work.
Then restore apps and data to the BB from a previous backup.