well, let me ask you this:
does your Xbox currently have some sort of dual-boot setup going on?
some of the softmod installers set it up so that there are two different pathes executed, depending on the DVD tray status when the Xbox is booted. to test this out, try turing your Xbox on by pressing the Eject button (leave the tray open for the whole boot-up process). if you get something other than your main dashboard (for example, MXM) then the next step is to see if this alternate dash is working properly, which is as simple as trying to log onto your XBox's FTP server. if you can successfully do this, then you have found a back door into your XBox should you manage to break your main dashboard in some way.
if you follow the above procedure and find that you have a working backup dashboard, it might then be as easy as replacing the XBE file for your dashboard.
rock.