Have a 2003 mercedes slk230, the ignition switch needs to be replaced but the key won't turn on, how do I get this to happen in order to remove the switch??

Dose the turn at all? On my old 560SEL there was a pin hole under the ignition switch it's self. But the key has to be in on position. Have you tried spraying it wirh WD40?

try another key- spray some graphite on the key- short of a quick fix, this is a job for a professional-

Jamnblues is absolutely right. If the quick fix didn't work gwt a locksmith. Otherwise you can have more problems then just a stuck key switch. Good luck.