WSOD on startup -- unless I start with Cmd-Option-P-R

I have been living with Mail not working for me on Mountain Lion but a new problem showed up in the last couple of days -- I get the White Screen of Death on powerup unless I start with cmd-opt-p-r pressed. This key sequence resets the NVRAM.

Now I have to reset the NVRAM every time I turn on the power otherwise it just hangs with a White Screen. I don't see the grey apple logo etc.

But if I start with cmd-opt-p-r then I get the double startup sound and the login screen.

What could be wrong here? This is on a 2009 27" iMac. Could it be that the button-battery (CR2032) that powers the NVRAM has been dislodged/died?