cant boot my mac, stuck on logo with loading wheel.

I don't really know how this came about but i installed windows xp on snow leopard and it was working fine. All of a sudden my mac was getting slow and then i just turned it off to get it back to its normal state but now when i try and reboot my mac just wont start up!?

what's happened and what can i do!

 

when you say you installed win xp on snow leopard, how did you do that? are you using bootcamp, or parallels? Or both? if Parallels, what version?

The first thing I'd do is insert the OS X DVD that came with your Mac (while the Mac is trying to boot), wait to see whether the Mac is now trying to boot off the DVD, and if not just turn your Mac off - then turn it back on but hold the "C" key until you hear the CD drive work a lot (you hear the head motor go back and forth). The Mac should now boot off the DVD. It'll take you to the "install Mac OS X" screen. Don't install OS X though - there should be an option at some point to not install OS X but to use other software on the disk. What you want is the Hard Disk Tool (or whatever it's called in English; I'm on a German system and don't have the System DVD right now as I'm on holidays). That will give you an option to repair the disk.