There is a lot you can do but I can be of more help if I know more about the problem. What do you mean it stopped working? It doesn't start? It doesn't capture? Something else? Which version of Fiddler is that? What OS?
Telerik by Progress
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Feedback Portal
and vote to affect the priority of the items