Im really hoping someone can help.

Today I tried to install the new OS for my Blackberry 8310, whilst it was downloading it said there was a fatal error and that things were lost but could be restored through the desktop manager restore option, however by this point the device had turned itself off and the indicator light flashing red twice, the desktop manager stated it had disconnected from the device.

So after checking these and many other forums it seems that the only solution was to do a wipe and reinstall the OS.

I tried to wipe using the JL_cmder, but that wouldnt recognise the device, I have tried the alternative method using the dos command prompt, however once i get to the point where i need to enter cd common files, it tells me the system cannot find the path specified, ive checked the folder i know its there, I cant understand why this wont work or what I can do next, I really need some help with this.

You can simply install the new OS over what you have and it should take care of wiping.

okay Ill try that, I didnt think it would work as the device doesnt seem to be conntecting to the desktop manager

You can always try a different USB port. That often helps.
Also, connect directly to your pc - not through a USB hub.
Restarting the pc can sometimes straighten out connection issues.