Problems getting Net access through switch

I am a basically a novice when it comes to networking

I have a new cable modem Cisco DPQ3212 and a TP-LINK switch
TL-SF1008D connected to the modem. I have 3 laptops and 1 PC
connected to the switch ACER (Windows 7), Dell Inspiron
(Vista), ASUS (Vista) and an ACER PC (Windows 7). I can
only get the internet on 2 of the connected computers, any 2
depends on which connects first. Each of the computers is
capable of accessing the internet if directly connected
through the modem. I am wondering how I can get internet
access to all 4 through the switch?

All computers used to have net access through one main computer when I had my old modem.

It's probable that your ISP only allows you to connect two devices. If you use a router with NAT instead of a switch then you will be able to connect all four computers because your ISP will only see one device (the router).

Thanks for your reply. I actually told the guy at the computer store what I wanted to do and he picked the switch for me, even though I had asked for a router. I didn't think too much of it because someone had told me do the same job. Just might have to go get a NAT router as you have suggested. Thanks again

from the info I could find on that modem [Cisco DPQ3212], it is only a modem [no routing capabilities]. So, Im surprised you got more than 1 pc to connect at same time.
As E-Oreo mentioned, you will definitely need a router instead of a switch in order to get all of your laptops and pc's connected to internet.
Or you will need to use a main PC with 2 network cards [as you mentioned at end of your post] and use Internet Connection Sharing [ICS] with your switch and modem [connected one on each NIC] to get everything connected.

Thanks for your reply

You can do it but first you must have 2 network adapter in 1 pc

so 1 of them used for ISP and the other for shared between computes by using

network sharing by Microsoft.

Thanks for your reply.

I ended up getting a 4 port D LINK router which 3 computers are now successfully connected to. I used a crossover cable in the 4th port to connect my D LINK switch which the other pcs and laptops connect through.

Thanks again everyone for your help/replies