Did you try to install DragonFly relatively recently and it never made it past the bootloader? Apparently there’s a bug in some BIOS when using a smaller USB drive to install. The loader checks multiple places for information, and if it checks somewhere that’s ‘farther’ than the end of the disk (i.e. 6G on a 4G USB key), the machine locks up.
Matthew Dillon and Kyle Davis spent a good number of hours figuring this out today, and Matt committed a fix. So, if you were bit by this problem, try a -LATEST image about 24 hours from now and see if it works.