Corrupt OS X Leopard installation...

Hey, so I was on my mac and I noticed that no applications would quit…even force quit. I attempted to use the restart and shut down desktop options, but to no avail. I proceeded to press the power button, which worked, but when I restarted I got the dreaded “You need to restart your computer” message at the boot prompt. I’ve tried restarting several times, but I get the same message. Fortunately boot camp still works, but I really need my os x install back (and I have neither tiger nor leopard install discs). I’d be grateful for any help. Thanks!