My IP for server network

I have a specific IP set up for our network and server and when we were using (another internet provider) we were able to go into the modem they supplied and change the settings to match ours. We just had Comcast set up with static IP and I am unable to change the IP address on the modem! So for the past 3 or 4 days we've had this new internet service we can't even use it! I calked customer service and he seemed like he's never encountered this question before but put me on a 24 hr ticket. I don't want to be forced to pay our outside IT guy $200 hr to come in and change all the network settings so they match the seemingly unchangeable settings in the new modem. The 10.1.10.1 won't work with our current network. I also need to disable DHCP as well but when I tried that it didn't help. What can be done?? What are my options?? I am really tired of turtle's paced DSL and really want to be able to start using Comcast because now I have to pay for both until I can resolve this issue !!