Heat Pumps and Electric Heating - york HP not turning on

Hi
Please we need some help with our HP....It has been working fine for 8 years (we had it installed new). I just figured out that the HP is not turning on anymore. I figure from the electrical bills it has actually been almost 2 months maybe. (We live in western Washington state and it doesn't get too cold here. however, this year it has....below 5 degrees a few days and below 30 degrees maybe 35 days this winter. A whole week of snow)

Anyways, I was trying to trouble shoot it myself and this is what I found out....
The emergency heat system works fine....nice hot air blowing on when I turn up the tstat. When in tstat is in regular heat mode the HP does not turn on and sometimes cold air blows through the register. I checked the breaker panel inside the house and the breaker is off. So I reset it. Still the HP does not come on. I check the outside breaker panel and it looks fine. Is there somewhere else I should check?

Why did the breaker trip now? Granted we live in the country and do have power outtages, also my dad was here and staying in his RV so maybe it happened then.

Just want to make sure that I don't have an easy/dumb fix before I call the repair man out here.
Thanks so much

I say call a tech to look at it if you dont know electric. Or go into the out door unit with a amprobe and see what is wrong Can be electric or freon also. Stat wire to the out side ok?? does the Ac run???? lots of IF's here..;)

Next thing I'd do is break out the multimeter. If you don't know how to use one its time to call a pro.