Does it say where it is looking for the boot device? floppy/cdrom?
When your computer starts, go into the BIOS. This is usually done by repeatedly press delete or another key when your computer starts. Look in the options for boot order/boot priority/etc. There should be three enteries, containing things such as harddrive and floppy. Please list them and the order in which they appear.
And make sure you don't have any disks, especially floppies, in your computer when you start.
What was you doing just before the problem started?