Need help setting up cables. (pics included)

Ok, I'm in over my head and I have no idea what to do. I humbly submit to you for help.

I'm a repair tech at a small computer company and I'm not overly familiar with networking. Our modem died a week ago and we just got a new one. The wireless works throughout the store, but the wired internet doesn't.

Here is out setup.
A is our modem
B is our wireless router
C is this cat5 cable splitter thing.
D is our Vonage phone system
E is this Cisco SR244 10/100 Switch

All of the Ethernet cables in the store come in from the left and are attached to the splitter. They then go from the splitter to the switch. The switch is connected to the modem from a single Ethernet cable, but it doesn't look like there is one specific port it is supposed to go into.

This is throwing me off, because on the wireless router there is clearly a WAN port that connects to the modem, but there is no such port on the switch, so I don't know how it redistributes the internet from the modem to all the jacks in the store.

The wireless router (and phone systems) connect directly to the modem and work.

When I plug all the Ethernet cables into the switch, only 1 or two lights come on. The rest stay dead. I assumed there was a break somewhere along the line, most likely in the splitter, hence why in the picture you can see one of the wires pulled out. (I was going to repunch all of them, but I don't have a punchdown tool)

Any thoughts? I'm at a total loss.

 

SOLVED!

The solution (for anyone else who might have this problem) was that the switch was not configured to handle DHCP, NAT, Firewall, etc. That was all being handled by the wireless router.

I ran a cat5 from the modem, to the router, THEN to the switch and suddenly everything worked!

 

Good work; I did have a look at your setup just after you posted but it looked a little more complicated than I'm used to, I was going to ask for a sketch