Today I tryed to insert my stylus but something inside the phone snapped and now I can no longer fit it in. Does anybody know how to fix it?

I guess I'll need to open the device and find out what is broken. What tools do I need to open the N900?

A Phillips 00 and a Torx 5 should do it.
However, judging from the questions u ask, u might wanna ask someone to do this for u, with some experience in these things.
U can permanently damage ur phone if u r not careful!

N900 service manual PDFs are out in the internet if you google for them. It shows detailed diagrams of how to disassemble your phone and where all of the different parts go. Be warned that there are a bunch of tiny bits and it's not for the faint-hearted. (and will probably void your warranty, if you've got one)

Or, MacGuyver solution: put something sticky on the end of your stylus and see if you can extract whatever is in there

There is a metal bit in there that is supposed to keep the stylus in place, that's probably what snapped, or just come loose. Some others have had a problem with it and it was discussed in this thread.

The metal tensioner came lose in my stylus holder so i took the phone' s cover apart, found the missing piece, looked up the service manual and super glued the small piece of curved metal with a plastic end back the way it was meant to go. it wasn't too hard

Well thanks a lot for the quick responses.

I bought the device 15 months ago so I believe it's still on warranty. I'll mail Nokia before I repair anything myself.