What error msg are you seeing? (look in your status window) Have you checked to be sure you arent ignoring the sender/file type/dcc in mIRC's options or with a script? You said you cant recieve incoming files... can you send files?
check these options: in file/options, dcc, dcc/folders and general/lock. Also look under control in the addy book (click alt key and the b key) under list type: ignore, to see if you have the person on ignore.
Best place for help with your router is the website for the manufacturer and the manuals, but some good troubleshooting and general info can be found at
web page re dcc ports, the default is 1024-5000, but you can change that range to whatever you map in your router, just be sure to put them in mIRC's options under file/options/dcc/options.
you also need to be sure that mIRC is able to get your external ip, not the internal one for your network.