if you see a little dancing cow moving, just leave it on that screen and go do something else. the first time it started up for me it took like 20 mins (its instant after that)

 

try to manually DLDI patch it.
You got the latest R4 kernel right?

(also, it should't take long time at all to boot up, some extra seconds if you don't got the directory on the root, but still not long)