Weird home network problem with AT&T broadband

Weird home network problem with AT&T broadband:

I used AT&T broadband for sometime now, and eveything was working properly, before I moved to a new location, and re-subscribed to AT&T in the new location, and built a new computer.

Here is my setup:
AMD athlon1600 computer with D-Link network card (I think).
LinkSys router/4-port switch/Wireless Access Point.
Laptop with a wireless card.
PC and Laptop running Windows XP pro.
RCA AT&T broadband cable modem.

Here is my problem:
I CAN connect to the internet from both my PC and Laptop, but CANNOT connect to the router setup page (at 192.168.1.1 or something like that), nor can share files in my network (THIS IS MY PROBLEM: I WANT TO SHARE FILES AND PRINTERS. I cannot even see the other computer in my network). I have my PC and laptop set to obtain IP automatically.
But when I set the IP on my PC (or laptop) to static (192.168.1.2 or something like that), I can access my router setup page, BUT CANNOT access the internet. The router is setup the same thing I used to set it up before I moved. (Obtain IP automatic, nable DHCP..etc.).

Also, when I obtain IP automatically in my PC, and can access the internet, I notice that my IP address of the PC is not in the 192.168.1.x form, but in a general AT&T form (like 12.256.x.y), and the laptop also has a different IP address. (The gateway they use is a AT&T form 12.x.y.z, not the router adress 192.168.1.1)...

It looks to me that I am not part of the home network (linksys router) network, but part of the AT&T network, where my PC and laptop have their own IP address, instead of aving local IP to my network.

I guess I am not that newbie, so I am sure that I have stuff setup properly (as I did it before many times).

How can I solve this.? Very annoying not being able to share files/printers...

Thanks in advance...