Switch / router install

Okay gang, new to the forum - please be kind.

Am a developer / manager by trade  - not a network guy per se. Am helping my friends who own a large restaurant. Like many small businesses, their IT has been thrown together and patched for many years leaving them with a hodpodge of "stuff" and none of it really working well together. Enter this project...

So...they have about 6 PC's, 2 printers, couple of laptops and a tablet or two. They also have a complete restaurant system that is separate from this project but that's for another post. Basically, this is a peer-to-peer network with DSL internet coming into a modem and then to a wireless router (R6400) which is handing out the IP addresses. It's also feeding 4 AP's out in the restaurant / banquet room and bar. The PC's and printers are either hardwired to the router or to a small hub hanging off the router.

Fast forward to today where I've built a rack with patch panel, shelving for other equipment and the modem and wifi router coming in from DSL. I also have a GS724T V3 switch I want to play traffic cop for all this stuff. The rack is in the main office with the GS724 and there is another small switch (GSS116E) for a small workgroup group in the next office.

Here's what I've done - please tell me what's wrong or what I need to do to make this work. Seems pretty straight forward but something isn't spelling C-A-T here.

1. Wire DSL modem to WIFI router (DHCP)

2. Wire WIFIk router to GS724T (Factory defaults)

3. Wire GS724T to GSS116E in next office (Factory defaults)

4. Plug PC into GS724T

- I get no connectivity to the GSS116E - cable tests fine

- I get no connectivity to the PC

If I plug those two devices into the wifi router instead, it works fine but when going thru the GS724T, it's stopping something from happening. I don't have any VLANS or anything setup now but that's my plan for the future but at this point I cannot even get the basic communication working. I am sure this is something I've done dumb on my end so please help me before you bust out laughing! I promise I'll take the abuse - just get me running someone! Thanks gang.