Basically either the string won't retract, or the starter won't engage with the engine (sorry I don't know the names of all the parts).
Sometimes, if I get everything tightened just right, it works. For a few starts, then it goes back to its usual tricks.
I've seen the string catch like in this video @1:06.
@1:36 he shows where his part is warped and ovalled, but mine looks o.k.
The other side looks good too.
The Husqvarana kit to replace this is nearly $50 on eBay, which is a heckuva lot considering the original parts didn't go 2 years without trouble.