I used Drive Genious to defrag my iMac 750 gig hd. I got an error message and now my computer will only start in Boot Camp to Windows. I tried using the Tech Tool disc that came with it, but it ignores my holding down the C key, and just starts again in Windows XP!
Can you see your OS X HD partition icon on your desktop? If so, right click on that icon and select Get Info from the drop down window. What does it show for space used and space available? You could also double click the icon to open it and see whats in there. It sounds like you may have inadvertently
erased that partition.