2008 V70 starting problems
 

Sometimes when I put the key fob in and step on the brake to start, nothing happens. There are no lights on the dash. I pull out the key put it back in and step on the brake. At this time the vacuum for the power brake has not turned on so I can't push down on the pedal. Of course then nothing works.
I was told to replace the brake light switch. I did so with an after market switch because I am cheap. It did the same thing.
I broke down and bought a genuine Volvo switch. It did not work either. HELP!

There is a good chance the Central Electronic Module (CEM) is the culprit.

I would also take a look at this troubleshooting guide https://www.youcanic.com/guide/volvo-wont-start-problem