|I think what Wanderer ment is the hardware you are using. Is this a Dell, HP or what? Also what is the model number?|
This error is saying that your harddrive is either no longer being reconized or you have installed a new boot device like (Floppy Disk, Bootable CD ROM, External Hardrive, Flash Drive or somthing that is trying to boot before the hard drive (or at leaste we hope because the other option is your hard drive went belly up and that would really suck).
The solution would be to go into your BIOS and change your Boot Order to make sure no other device is set to be bootable other than you hardrive or you could simply change the order so that your harddrive is on top.
Also, if you BIOS has a built in harddrive diagnostics, that is non-distructive, you may want to run it to check up on your harddrive's health.
This is why Wanderer wants to know what kind of system you are using so we can give you more specific instructions like how to get in your BIOS.