Clearing NVRAM on Yosemite shows password entry When I make the ⌘ Cmd+⌥ Opt+P+R it shows a dialog with lock symbol and to proceed I have to give the password but this way I'm not able to proceed with the resetting of the PRAM. How can I reset the PRAM with this kind of obstacle?

I have a 2008 iMac with Yosemite.
You can also from the terminal in Yosemite run:

sudo nvram -c


and then restart the computer.