Flashing question mark at start up?

[tai27]

Today I turned on my Macbook Pro and all that was displayed what a flashing question mark, what does it mean?

 

[miles01110]

It means it can't find the startup drive containing OS X. Try booting from your restore disc or a retail copy of whatever operating system you have.

 

[tai27]

Tried booting CD from an external DVD drive (built in mac DVD drive suddenly just died SIGH) and all I get is either the spinning thing spinning forever or it automatically switches off.