LIke ITASOR said, the machine is failing to find an OS on any local disks.
You need to boot off the CD-ROM with your original OS install CDs (you may need to hold down the "C" key when booting to force the computer to boot from the CD). If the machine boots successfully, then the problem is either some corruption of the OS or a bad hard drive. You'll know which because if the hard drive is still visible on the desktop it is probably OK. Run "Disk First Aid" (in the utlities folder) to check the hard drive.
IF the hard disk seems OK, back up your data (on a floppy, an external HD, Zip, network drive or whatever) and try reinstalling the OS (I'd recommend the "clean install" option). If that works, and the computer boots off the hard drive, put your data back and go on your merry way.
If the machine boots off the CD but can't see your hard drive, try running Drive Setup and Disk First Aid (both in the utilities folder, I'm assuming you're running OS 8.x.x-9.x.x) to repair/reformat your hard drive. Then reinstall the OS.
If you can't reformat the drive and still can't see it, you may have a dead hard drive.
EDIT: xsedrinam has a good point - if you have or can get Disk Warrior I recommend you use it. It has saved my butt a few times, and may be able to fix your problem.