Currently Being ModeratedJul 11, 2013 11:38 PM (in response to Brianna715)
Welcome to Apple Support Communities
As I see that your iMac has got Leopard, call Apple to get replacement DVDs > http://support.apple.com/kb/HE57 They will give you the DVDs to reinstall OS X, because Leopard can only be reinstalled from the DVD.
After getting the DVDs, insert the Mac OS X Install Disc 1 and hold the C key while your Mac is starting. Then, choose your language, go to Utilities menu (on the menu bar) > Disk Utility, choose Macintosh HD in the sidebar, go to Erase tab and erase the disk.
Finally, close Disk Utility and reinstall Mac OS X. Open > Software Update, and install the latest version. Also, iLIfe apps are included in the Mac OS X Install Disc 1.
Another option you have is to upgrade to Snow Leopard if your Mac is supported > http://support.apple.com/kb/sp575 You can buy it from the Apple Online Store > http://store.apple.com/us/product/MC573Z/A/mac-os-x-106-snow-leopard The steps to install it formatting the hard drive are the same, but you will have a newer Mac OS X version