Q: I turned on my computer and I'm seeing a grey screen with a picture of what looks like a folder with a question mark on it. Help??

That means no boot volume can be detected.

Try smc and pram reset.

Boot from your installer dvd or recovery partition and run Disk Utility to try to repair/verify you boot drive.

A flashing question mark appears when you start your Mac

OS X Lion: About Lion Recovery

Which OS are we talking about here?  Lion or Snow Leopard or older?

At least try the smc and pram reset (follow links to see how).,

Then that Apple article on booting from the Lion recovery partition should bee what you need:

OS X Lion: About Lion Recovery

Basically boot with the command and R keys pressed.  Then you should be able to run Disk Utility from there to repair/verify your boot disk.

Still try the smc and pram reset.

Here's another article:

How to Boot into OS X Lion’s Recovery HD Partition

Generally you push these key sequences immediately after you hear the boot chime.

(it's my bed time, good luck)