Shianeh, welcome to the forum.
When requesting help you should always include the make/model of the computer and/or monitor. This information is necessary for us to review the specifications of them.
Once I have the model of the computer, I will do my best to help you solve your problem. In the meantime, here is a guide to help you check your hard drive. A failed hard drive is one of many reasons for this error message. Also, check the boot order in the BIOS to assure that it is not trying to boot to a non-system drive.