Will a 2006 mac pro run on a single processor?

[alfie9]

My 2006 mac pro, running yosemite, recently stopped booting altogether ... blank screen, no chime.

I noticed the CPUB FAIL led diagnostic light was on (red).

Have removed CPUB and still doesn't boot, no chime, black screen and no diagnostic led are lit. So am wondering if it does run on a single processor?

Thanks in advance!