Circle with a line through it on startup

Occasionally when I restart my Mac, instead of the Apple symbol, I'll get a circle with a line through it on my screen. The Mac just kinda sits there trying to load. Then if I power off and back on again, it will start up fine.

Any ideas?

Before doing anything else, make a backup of your entire hard drive. Use either Time Machine or cloning software - (SuperDuper or Carbon Copy Cloner).

The next thing to do is a FSCK on the hard drive. Boot your machine with the original install DVD, select the top menu item "Utilities", "Disk Utility" and do a verify and repair on the entire hard drive. Also run the repair permissions option while you're at it.

The reason for all of the above is that your hard drive might be acting up, thus it's best to find out now before data is lost. Don't forget to make a backup first!

Regards.

Howdy Thanks for the help. I've pretty much done all that stuff already. I've got 4 hard drives and only 2Tb of backup so it's taken several days of backing up and repairing etc.. All 4 drives read as being ok now but occasionally that circle thing appears again.
I can't seem to pin it down to one particular drive because it's so intermittent.
I'm thinking that one of the drives might be close to failure but otherwise works ok... hence, I was wondering if there was any specific description for what the circle with a line through it meant.
I've been using Macs for about 20 years and never came across it before.

The circle with the line through it means the system can't find a bootable device. That's why I suggested your hard drive may be failing. But it sounds like you're on top of it.

Regards.

Yeah, I was kinda figuring it the circle thing might mean that. I'm thinking this may be a more serious problem now... I've got 3 bootable drives & I'd assume if it can't find the first bootable drive it would automatically find the next one. Sometimes it just sits there with the Apple symbol displayed on a white page. Next time I get the circle. Next time it might boot up to my second drive. Next time it works fine.

Last time it did it, I was going to insert the Snow Leopard startup disk to see if that would work, but I can't see any way to get the CD tray open until the system is loaded.