Connectivity issues

> [...] my service providers modem [...]

   Maker?  Model number?  Is it a simple modem, or a modem+router, or
what?

> [...] plugs into my ac1900 router. [...]

   What, exactly, "plugs into" what, exactly?  (Hint: If a device has
different types of ports, then "connected to device" is not enough
detail.)  Usually, with Ethernet, cables "plug into" things; devices
don't "plug into" other devices.

   "AC1900" is a speed, not a model number.  Look for "Model" on the
product label.

> [...] From this router it goes to my AC2100 which is just an AP. [...]

   "it"?  What, exactly, did you connect to what, exactly?  (See "Hint:
[...]", above.)

   "AC2100" might be a speed or a model number.  Which is it?  Look for
"Model" on the product label.

> [...] Tried adding the 24 port switch from the AC1900 [...]

   "added"?  What, exactly, did you connect to what, exactly?  (See
"Hint: [...]", above.)

> [...] green lights on but nobody home. [...]

   _Which_ "green lights on"?  What, exactly, does "nobody home" mean to
you?

   None of that is a useful problem description.  It does not say what
you did.  It does not say what happened when you did it.  As usual,
showing actual actions (commands) with their actual results (error
messages, LED indicators, ...) can be more helpful than vague
descriptions or interpretations.

> [...] Anybody know where I screwed up?

   With my weak psychic powers and descriptions like "green lights on
but nobody home", I wouldn't try to guess what you did, let alone what
you did wrong.

   What happens if you leave the switch out of the picture?  Can you get
all the trouble you need without it?