Frozen Yeast

I live in the Chicago berbs and received a shipment yesterday from Minneapolis which included a bottle of WL 400 Belgian Yeast. Due to bad weather it took 2 extra days for the shipment to arrive. Tthe yeast sat in an unheated truck for 4 days at near zero temperature and when it arrived it was frozen solid. I thawed it out and prepared a starter. After about 20 hours I can't tell whether the yeast is dead or alive. My question is does frrezing kill yeast and would I be better off buying some more yeast and be safe. I hate to wreck a whole brew by pitching dead yeast. I know there is another thread covering starters but didn't want to hijack the thread.

Freezing will kill liquid yeast. Since it was a hard freeze, I think you'll need fresh yeast. If it had been 25F or so, there would be a good chance of revival, but not at 0F.

Yep. the problem with freezing is that the water will crystallize and puncture the cell walls of the yeast. You may be able to nurse a few surviving cells to a decent culture but it's too risky regarding infection, takes too much time and may never actually become a viable culture. It would be much easier to simply get good yeast.