Reboot into Safe Boot: if using DellEFI 1.1, press any key when it counts down before the gray screen with the Apple logo and type: -x
if using a newer version of DellEFI I believe you hold the Shift Key during boot. You should see "Safe Boot" at the login screen (if you have one).
Then run DellEFI, select custom install and remove the hardware specific dsdt.aml file (it may be the only option selected, this is good). Once this is completed, reboot again into Safe Boot using the above steps. Then rerun DellEFI, choose custom, then check Reinstall mini9 Extentions and check regegenerate custom dsdt.aml file. (Those two should be the only items selected) -- once this completes, it will ask you to reboot, select yes and reboot like normally. Hopefully you're problems have been fixed and you can now login
Once you login, you may want to Repair Permissions in Disk Utility (this may take about 30-40 minutes).
The above worked for me anyway