Q: my microsoft office 2011 just stopped working on MAC Yosemite

Since it is a Microsoft product post in their forum:

http://answers.microsoft.com/en-us/mac

As a perpetual license product, there's no expiration date at all. It will keep working on any computer capable of running it for eternity. What would likely run out in October of 2017 would be all product support. That is, no more software updates or technical phone/email support.

I tried using my log in and it wouldn't work.

What login? There is no login for Office 2011. You install it from the DVD, enter the product key to activate the suite and that's it. There's nothing that needs to be entered each day in order for it to operate.

Are you talking about Office 365?

Same question: what login?