Cannot find disk at startup

Hi,

When I start up my PowerMac desktop running 10.5.8, I get the spinning icon at the initial gray screen, and it sits there forever, unable to locate/recognize the startup disk (which is one of two disks in a partition). The workaround I've been using is to pop in my Disk Warrior CD, allow that to start up (until it recognizes the drives), then to quit and restart while holding down the mouse key. Any suggestions on how to bring this back to normal, like it was about a month ago?