This should help you out for fixing your phone.
How do I wipe the BlackBerry using Jl Cmder? - BlackBerryFAQ
and
What to do next if Jl Cmder will not connect and wipe - BlackBerryFAQ
I'm not 100% sure if it will help in installation but I would upgrade your 8700 to OS 4.2 (if you haven't already.)