Help! iMac G5 won't boot up to HD

Ok so today I am having quite a distressing/unexpected/random problem with my iMac G5. Here goes: Today my friend and I were working on a project in iMovie, running Photoshop CS, Firefox, etc, all in all working the computer out to a fair extent. All of a sudden, the computer started getting really realllly slow, and photoshop locked up and did not respond, so I had to force quit it. I quit things like preview and firefox as well, and we said why don't we restart the computer maybe to free some things up. So I manage to quit everything and get to the desktop, at which point the computer informed me that two of my widgets had crashed, I believe they were the iTunes control and some lyrics viewing widget I have - both of which I have been using for a long time without any trouble. I said alright and I went to restart, and when the finder (dock, bar) things disappeared, it got stuck at the desktop picture. Now it's usually pretty fast shutting down, but not this time. We waited for a minute or so, and then I shut it off by holding the power button on the back, which I have not had to do for ages. (I got the computer almost a year ago). When I turned it back on, in the bootup screen instead of showing the apple logo, a little blue folder came up with a finder icon and a question mark flashing on it alternately. It stayed like that for a long time, so I inserted my Tiger disc and restarted, holding down the C key and booting up from that. I went into Disk Utility, and it had renamed the hard drive "disk0s3", instead of the usual "Macintosh HD" name. Also, it says that the disk was currently Unmounted, and all first aid attempts failed. Out of curiousity, I went to the place on the disc where you can install OS X, went through some of the steps, and when I came to the step where it asked me where I wanted to install OS X there was nothing there. No hard drive icon - nothing. Very strange problem. Also I might add, when I leave the computer with the flashing finder folder/question mark bootup icon for a few minutes, after a few minutes the fans come on full blast, and stay like that until I shut it off. Btw, up until this the computer had been running beautifully and quickly, with no strange problems that would have led me to believe that anything was going to happen.
Could somebody help?

I had the same problem with my mini once, it seamed like the hard drive must of stopped as when I went to open the widgets the whole system locked up and the same problem as your came up, how I fixed it was the darndest thing, I hooked it up to my TV and magically it came back to life! It hasn't had a problem since but I have no idea what happened!

As for your problem I don't have any idea unfortunatlly at the moment. Sounds like Hard drive failure, remember to back and back up often.

Yeah, I actually plan to try to use my iPod as a boot disk and see if I can get anything off the hard drive.. but I'm being somewhat optimistic, but still worth a try. Regardless if that works or not, I still don't know how to get the hard drive working again! (I think I have to mount it or something; it says it's unmounted, but as to how it got that way I have no idea!)

Actually, I booted up to panther with my ipod last night and I also ran the hardware test cd - apparently my hdd is seriously messed up. So today I took it into the apple store and fortunately the repair will be covered under the complimentary warranty. The only bad news is that all of my stuff (other than music) is gone! Oh well, it just reminds me to back up...