OK I am a twit..
I have 3725 router with internal CF and external slot for CF.
I tried upgrading and ended up deleting the iOS version on the internal flash, and can not now put the iOS back!!
Even more stupidly I turned it off.... so there was no active iOS..
I have tried formating the CF card on an 1841 but the 3725 won't read it...
DOH. IT is obviouslly stuck at ROMMON
Please can some helpful person advise on the correct way to format a CF card so my 3725 will read it and I can get an iOS back on it!!