Hi,
I recently got a renewed machine (inspiron 660s) from dell.
The start-up screen always shows "manufacturing mode", even after I entered the service tag.
I tried many keys to try to switch back to normal mode but did not work out.
Finally, I pressed "Load Defaults" on the Exit Menu and then Exit BIOS setting.
Everything became normal then. A Dell Logo appeared on start-up. (Afterwards of course I can change any settings :)
Hope this help!!
Mario :D