Disconnect the printer and uninstall drivers and software, restart the pc without it.
Do a complete shut down, then start up without connecting printer. Now run the install choose custom instalation (hopefully that's an option) carefully follow instructions.
At some point there may be a window pop up showing which port it's going to use, see if there is a way to change it this point, if it's using the same one as before try changing it, if not cross your fingers and hope for the best.
I take it there was nothing of help on the Dell site?
If it doesn't work now, find a big hammer to kick start it.