I'm having trouble waking up five begonia tubers, and I'm wondering if I should just give up and pronounce them dead.

I overwintered three of the tubers, and these are all quite small -- about the size of a quarter; the other two are large tubers (4 inches or so) that were purchased only a few months ago (from Hirts.com). Two of the small tubers are the "On-top" variety, but I don't know what the third is; the large tubers are a Skagum and a Daffodil-type.

I've had all of these in my 66-degree laundry room for 3 weeks, and they haven't broken dormancy. I even gave them a hot-water bath about a week ago(following the directions given on the Canadian Begonia Society's webpage). They're being stored in individual bags in a cardboard box. All of the tubers are firm; there are no mushy spots.

Am I doing anything wrong? Do the tubers need light to break dormancy? Is there any way to determine if they're dead? Or should I just stop being an impatient newbie?