remote desktop not working after modem change

about 2 weeks a go my internet connection was very slow and intermitant. I called and comcast send in a tech and he rep-laced my modem. I was able to remote desk top to my PCs but after modem replacement I am not able to do remote desktop any more.

- The present modem is an SMS business IP gateway.

- I have static IPs and computers are setup with static IP and thats is thet way I was doinf remote desktop.

- From remote computer I can ping the IP address that is assigned to default gate way. But I am not able to even ping the IP addresses assigned to computers.

- I did try palying with the setting on the modem firewall/port forwarding however when I try to give any of the IP addresses assigned to me to allow port forwarding for port 3389, it saya the IP address is not correct.

- I should say hat I realy do not know what is the correct setting for all the options on the firewall section either. I just read theings here or there and tried different things and I am at  the poinr of frustration.

I realy appreciate if comcast people read this and can remotly setup my modem appropriatly so I can do the remote desktop. Or some one give me detailed instruction as how I can fix this issue if it is the modem setup issue.

Regards, Farid