problem after deleting windows partition

ok, so my mom has an imac with the intel chip, and we tried to put windows on her computer. i made a partition and started installing windows, but i didn't have the serial # with me at the time so i couldn't finish. after that, her computer was starting up in windows trying to finish the install, and she decided that she really didn't need windows on it after all. we deleted the partition. now when she starts the computer it asks for the os x install disk, but if we hold option, it will show the os x hd and start up without the disk. we can't find the os x disk, is there some way to get it to just start up like normal without the disk, bypassing the need to hold down option?

you have to go to
system preference, then startup disk, then make sure your osx bootup drive is highlighted before you exit. This should fix it!

cool, i'll give that a try, thanks!