Static Ip w/ smcd3gn router



Was wondering if anyone could help me with a small problem. My xbox and my computer can never be online at the same time because both of them seem to have the same ip address when logging onto the internet. I’ve searched countless of sites and I do know how to assign static ips to my computer and my xbox, but it never works. I think it’s cause my ip isn’t the usual format, its more on the lines of 99.2XX.XX.33 (the x’s are numbers), I also have a hunch that my router isn’t masking my ip therefore thats why its not starting with 192? I dont really know computers so please help!