You haven't mentioned any type of troubleshooting steps you have taken up to this point and also no information about the computer (desktop vs notebook) so if I list anything that seems like a no-brainer to you, remember that others may benefit from the thread as well.
Put an old hdd in your system and test (if available)
Test the hardware components in another computer (if available)
Reset the cmos - u can use the typical method of switching the position of the cmos jumper. Refer to the manufacturer of your computer, or the manufacturer of your motherboard. Whichever is appropriate in your case. I have found at times this is not enough, and that removing the battery from the motherboard for 30 seconds to a minute is the most complete method for clearing cmos.