Didn't figure it would be to hard but I missed the first step turn the power off, replaced my mother in laws theremastat and now a.c. won't kick on with the new thermastat or the old. Read previous advise and can't find fuse... what now?

Does the heat work?
Fan work?
Is it the inside and outside unit? AC will take about 5 minutes to come on after being powered up.

Or is everything dead?

Wired wrong,, or may have blown the transformer,, or both