1) Remove any USB devices plugged into the computer and any CDs in the drive.
2) Check BIOS settings and ensure your primary hard disk is first to boot
3) Put a Windows disk in you computer, assign the BIOS to boot from CD first, boot computer from windows CD and start the install process untill you get to the disk setup section. Does the windows installer see your hard drive? (This only works with actual windows disks, not OEM restore disks) If it does see your disk, you can re-install windows without formatting or deleting your files. Once windows is installed, all your old files will be located in C:\Windows.old\
If you have an OEM recovery disk that doesnt have the official Windows Installer one thing you can do is install Linux onto your computer. Once linux is installed it will fix your Windows partition. However this isn't recommended as you will now have linux and windows on your computer and it will ask which one you want every time you boot up. It will also repartition your drive and you will loose some storage space.
There are more options (better options) available to you if changing the BIOS settings and removing all USB devices and CDs / DVDs doesnt work, so be sure and let us know what happens.