Hi there bunminaomi,
You have an OS CD right?
You can reformat your HDD through the command prompt and reinstall OS afterwards.
- Once you are in Windows setup, press shift+F10 to bring up the command line.
- diskpart [enter]
- list disk [enter]
- select drive [number] [enter]
- clean all [enter]
- create partition primary [enter]
- select partition 1 [enter]
- active [enter]
- format fs=ntfs [enter]
- assign [enter]
- exit [enter]
- exit [enter]
Keep in mind that you will loose your data, as you will reformat your drive and install OS.
Cheers,
D_Know_WD