Computer Doesn't Turn On
If the computer doesn't turn on at all, check all your switches and plugs. When a switch is labeled I or O, the I means On.
If you have a floor surge-protector bar with an on-off switch, it may have been kicked to the off position--make sure it is on.
If you have any other devices attached to your computer, such as a scanner, hard disk, or CD player, sometimes they must be turned on first or sometimes they need to be turned on in a specific order. Try changing the order.
There used to be other things that could prevent a Mac from turning on, but if you're using Mac OS 9, you don't have one of the older machines or older problems.
You see the Question Mark, the Flashing X, or the Sad Mac on Startup
Ideally, when you start the computer you see the Happy Mac (Figure 8). This means all is well. Sometimes, though, you may see another icon, like the image of a disk with a flashing question mark (Figure 9). This is a visual clue that the Mac cannot find the System Folder. The System Folder must contain the System file and Finder file. If you are using an external hard disk, make sure the hard disk unit itself is turned on and is up and running, and make sure any extra switches are also on. If there are any other devices attached to the computer, they sometimes have to be turned on first. When you start attaching a lot of things to a Mac, they start getting fussy about the order they're turned on.
Figure 8 The Happy Mac. We like this guy.
Figure 9 The flashing question mark.
The disk with a flashing X (Figure 10) means the Mac found the disk you thought was a startup disk, but it really isn't a startup disk. There may even have been a System on it, but the Mac can't use it. Try your other startup disk (see below).
Figure 10 The flashing X.
The icon you really don't want to see is the Sad Mac (Figure 11). This means there is something really wrong and you probably need your power user friend to help you figure it out. Even more serious is when the Sad Mac shows up on a black screen (rather than gray or colored or patterned) and plays the Chimes of Doom for you. On the black background, it looks like a Dead Mac. I, personally, have heard the Chimes of Doom six times in my life, although it has been years since I've heard them.
Figure 11 The Sad Mac, better than the Dead Mac.