Firstly type /sreq ask and see if that helps, quite a long shot though.
In 95% of cases, DCC receiving issues are caused by the person sending the file. Usually if you can send, then there is no problem at your end. However, the only time I have seen the DCC accept dialog not showing up is when 'weird' ports are set for DCC. What ports do you have set for DCC? Do you have a router? Try getting a file from several of your friends, not just one/two, and see if any of them can send to you.
Other ideas about what can cause DCC get issues can be found in the [url=http://www.mirc.com/faq6.html#section6-10]mIRC FAQ[/url. You may also want to use the Search feature and see if you can find a solution.