✦ Starter Troubleshooting ✦
Before anything else: how old is she, and how warm is your kitchen? Those two answers solve most of these.
If she's less than two weeks old, this is normal and it usually isn't a problem. New starters go quiet for days at a time while the culture sorts itself out. Keep feeding on schedule and wait.
If your kitchen is below about 70°F, she's cold, not dead. Cold starters ferment slowly and may take twelve hours or more to show much. Move her somewhere warmer, on top of the fridge or in an oven with just the light on.
If she's established and warm and still flat, try this for three days: discard down to a spoonful, feed at one part starter to five parts each flour and water, twice a day, at the same times. Use whole wheat or rye for at least part of the flour, which ferments faster than white.
Check your water. Heavily chlorinated tap water can suppress a starter. Leave it out overnight or use filtered.
When to actually worry. No activity at all after two weeks of consistent twice-daily feeding, in a warm spot, with fresh flour. That's rare, and starting over is usually faster than rescuing.