Try erasing the Main Load and booting... You must have option 43 or 128 setup correctly or it won't work. This will erase the main load from the device, and then write it manually from the FTP server. Note that this could brick the phone though, so try one first and be prepared to trash it if it fails.
Hard to say if it will work... I haven't had a Mitel running 4.0 software in over 8 or so years. This software was released in 2009, and support for it ended in January of 2013 when 6.0 was released. You should really get this one upgraded to 8.1 at least.