1. When you say "not responding", does that mean a message from Windows (which in English anyway uses those 2 words) saying that the program has got stuck? If so, there may be a problem reading the source file.
2. If not, is it that the source text has been moved?
When Concord wants to re-access the source text, that does depend on the whole disk access system working OK. Access over a network can easily get disrupted or slowed down. Local access (on the same PC, or on a memory stick in that local PC) is usually reliable.
First thing to check is: does the source text seem to open up OK? If it does, re-boot and try again. Hope that helps!
Cheers -- Mike