Issues with new modem - CM1200

> [...] I currently have a TP Link N450 Wirless Router and it has no
> issues, and a Netgear G54 WGR614v10 and it won't connect. [...]

   Are you connecting them one at a time, or (in some way) at the same
time?

> [...] It keeps saying it's having issues detecting the internet
> connection. [...]

   Copy+paste of the actual message might be more helpful than your
interpretation of the actual message.  Your ISP might not cooperate if
you change routers without a complete shutdown and restart of the modem
and router.

> [...] it seems to not be working with a ethernet splitter I have set
> up, [...]

   Where, exactly, did you put it?  What, exactly, is connected to what,
exactly?  (Hint: If a device has multiple Ethernet ports, then
"connected to device" is not enough detail.)

   Terminology: "network switch" (or "hub") is a well-defined entity.
"Ethernet splitter" is not.  (Does it say "splitter" on the device or
the package, or in the documentation?)

> [...] it's only providing an internet connection to one PC instead of
> all four, the model is a TP Link TL-SF1005D 5-port switch. [...]

   If you're connecting your switch directly to your modem, then don't
do that.  Most likely, your ISP will provide only one IP address to
whatever you connect to your modem (first come, first served).  A NAT
router is what allows you to use multiple devices with your one-address
Internet service.  A network switch (or hub) is not smart enough to do
that.

   You should be able to use your switch on the LAN side of your router,
but not on the WAN/Internet side.

> Are there any routers and ethernet splitters that work best with this
> modem?

   Practically any (working) router should work with it.  Connecting any
network switch directly to it is probably a mistake.