unable to load os?

I just built my computer yesterday, it booted up perfectly installed the os, opened and closed it for a bit, then the next morning i boot it up and it says, "unable to load os" I did reset the cmos before powering up if that makes a difference?

Try going into cmos and make sure that the boot device is set properly. Determine which device is the boot device and enable that somewhere in the boot device priority.

If that doesn't work, boot your windows cd and when you get to the selection screen, press R to enter the recovery console. Verify that the windows installation exists at this point. If you can enter into installation drive under the recovery console, you might consider trying fixmbr or fixboot. First check that your filesystem is intact. Make sure that the boot.ini file is in the proper place.

Check you did actually hook the drive back up when you were messing around inside