Hi ednelsonYY,
· Are you able to boot to the desktop?
· Have you made any changes on the computer prior to the issue?
· Do you get any error message?
· What is the make and model of the computer?
Check in BIOS whether the hard drive is detected or not. Make sure hard drive is set as the first boot device.
BIOS: frequently asked questions
http://windows.microsoft.com/en-US/windows-vista/BIOS-frequently-asked-questions
Note: Modifying BIOS/complementary metal oxide semiconductor (CMOS) settings incorrectly can cause serious problems that may prevent your computer from booting properly. Microsoft cannot guarantee that any problems resulting from the configuring of BIOS/CMOS settings can be solved. Modifications of the settings are at your own risk.
If you are not comfortable changing the BIOS settings suggest you to contact the computer manufacturer for more help and information.