if i install mirc irc links work, but if i make my standard configuration they don't work anymore. could it be that i deaktivate them accidentially?

Without mIRC installed (or some other client that accepts irc-type links), how could your computer know that those links are meant to be interpretted by an IRC client?

I'm not sure what you mean by "if i make my standard configuration" but if you mean setting up your options how you like them goto the Options menu, and under "IRC" select "Catcher" and make sure the box on the right that says "Enable support for chat links" is checked.

File - Options - General - [ ] Hot links ONLY when shift key is pressed.

You want this NOT checked.

File - Options - (double click) IRC - Catcher - [x] Chat Links, enable support

You want to check this.