Did I understand you that you said you switched motherborads, and the problems began? If so read on.
One thing to try before you pick one of my suggestions below is; go into your bios, make note of the settings, and then set everything to default, if it works, great, if not, you know the settings, and can set them back.
Well replacing a motherboard is one of the reasons why an existing install of windows wont boot up. There are many things different from one mobo to the next. Often it is a good idea to back up all of your data you want to save and reinstall windows when you make major system changes, and chaning motherboards is one of those.
If you have the old motherboard put that back in, and most likely you will be able to boot into windows fine. Then back up your data, wipe the drive and install windows with your new motherboard installed.
Or you can get another hard drive, if you dont have one already, and install windows on that drive, and put the previous drive as a slave and access all of your saved data.
If you dont have any data you need to save, then just put the windows install disc in and go through the install process, I would suggest that you format the drive first, rather than installing windows on top of its self.
Hopefully one of those will work for you.