OSX Problem

Hi all,

I have encountered a problem with my iMac where the symptoms include 1. refuses to switch user all of a sudden 2. the mouse's wheel function on the magic mouse stops working (can't scroll up / down a webpage). It's like some of the features just suddenly stop working. I still can't figure out what causes it to happen to begin with.

It can recover itself once I force restart the machine, but if there's a better way to recover, that'll be great!

Thanks gurus in advance!

Don't know if this will fix it, but I would try repairing disk permissions, booted from your install disc.
Boot with the disc in the machine holding C as soon as you hear the tone.
Once booted, select language and then go to utilities/disk utilities in the menu bar, select your HD and repair disk permissions.