Either your loading from the wrong hard drive or your Windows installation is corrupted. I would check your boot sequence and make sure that the hard drive with the OS on it is listed first.
Then if it is you will need to put your Windows cd in and do a repair so that it loads the BOOTMNGR file and your Windows will then boot into the desktop.
How long have you been using the computer with this operating system installed ?
Is your omputer a desktop or laptop ?
This is a duplictae post and it isn't necessary to make multiple posts since you will get duplicate answers from people who haven't read the other post.