I guess something happened during the installation that messed up your boot management.
If this is the only problem, then everything should be back to normal when you restore a boot manager (doesn't even have to be Windows).
Run the installation disc again to fix your Windows 7 Boot Loader.
Select "Repair your computer" when the installation main screen comes up.
Select the right OS (you probably only have one, so no confusion here), then go under Command Prompt when given the chance.