5 year old iMac will not boot up. Had to restart following a software update from Apple. Tried soft boot, zapping the pRAM nothing has worked. Any suggestions? All I get is a gray screen with one spinning gray icon (not even the beach ball!)

Insert your Mac OS X disc, either a retail copy or the one which came with your machine, restart the machine and hold down the 'C' key to boot from the disc. Follow the on-screen instructions to re-install OS X.

This is basically my exact issue. Last night, 03/25 my Imac G4, 800mhz, 768 ram,10.4 OS, and 50+ gig hard drive worked fine. I wanted to go into the system preferances and change the sleep time my hard disk would take before sleep. I accidentally hit the software update button. Low and behold, there was an update for software. I said to myself I'll do this update since they recommend it. I do the update and restart my computer and that's when the mess started. I can get the gray apple screen and the little sunburst thing. Get to the other window where it says Mac OS X and then nothing happens. Cd wont boot or anything. Wont read disks or anything. Even after manually opening the drive and inserting in a disk, holding down the c key and so on. I even did those command things nvram and reset all. Even some more I don't remember which ones. Some even before I came to this site by accident. Nothing will seem to work.