If you have time:
Defrost the pack in the fridge for about 6 hours, then warm up to 68-74F in some tepid water, and add to 1 liter of freshly made 1.020 starter wort (not the usual 1.037/1.040), and put her on a stir plate for 2-3 days. If you see the starter beer getting much lighter in color from when you started, usually after 24 hours, she's alive (!) and let her continue. Otherwise, let her go the full 2-3 days, then check if she got any lighter. If not, start over with a fresh pack or exercise more patience, up to a week.
That's step one.
You'd need to cold crash for a few days in the fridge, decant the (mostly) clear starter beer on top, then step up the slurry one more time in a 2 liter starter for a good pitch.
Yeah exactly what Lizards said, I had my hefe yeast literally take 3 days to wake up from being frozen(glycerin/water) but it came alive and went from brown to almost neon yellow, so its happy now and doing its thing.
The color change from medium brown to significantly lighter, and even creamy looking, indicates more yeast cells are in suspension.
There should also be a significantly larger amount of yeast precipitated on the bottom when not stirring/swirling, compared to where you began.
You can take a gravity reading of the starter beer after a few days using a hydrometer or refractometer.* If the result is lower gravity than from where you started, there was fermentation, IOW the yeast is not dead, but it still doesn't indicate how vital/viable she is, how many cells are alive.
You could do a cell count under a microscope. That's much, much more involved than observing color change in a starter or the forming of a thick yeast cake on the bottom of your starter vessel.
When the starter is done you could pitch the whole starter as is. Or cold crash in the fridge for a few days, then decant the mostly clear starter beer off the top leaving the thick slurry behind.
Thx, looks like it works, 2 days after starter is milky yellow. Will repitch it with proper wort but now i'm very optimistic about fermentation Almost throw yeast pack in trash when i get it from a freezer.