You *have to* install the Handheld OS for the 8310 onto your PC in order to load software.
Look in the top of the 8300 forum and it will give you the location of the latest 8310 handheld OS.
Follow the instructions on
Main Page - BlackBerryFAQ on how to load a new OS.
That will get it working.
THIS IS NOT A DESKTOP MANAGER ISSUE - do not download and reload DM.