Conflicting Gateway address with Wireless USB Data Card on Network

I have a dilemma where I have a network of 2 computers and a copier on my router. Everything works fine. Once I put my Wireless USB Data Card into my main computer, the internet will only work when I have my internet connection shared on the data card and it then tells me that my main computer IP address will have to be reset to 192.168.0.1 in order for it to be shared. Once I share it, the Ip address of my main computer resets to 192.168.0.1 and the gateway address to my router disappears. I try manually inputing my gateway address of my router to my local area connection but then my internet stops working. I called ATT(which is my internet provider) and they said it s not possible because my data card needs its own gateway address, (which makes no sense to me). So at the moment its either use my internet or connect to my network and they say I cant have both at the same time. Please help me with this.. I know its possible. I tried also putting the gateway address of my router on my wireless connection but it doesnt work. Im a printer so I need my Copier to print yet I need my internet to access the files to be printed. HELP fix conflicting gateway address problem!

By the way, when I have the already added the gateway of my router to my local area connection and my wireless card has its own gateway address. They both ping and are connected but the internet stops working.