As I understand it you installed Win 7.
Did you do a clean or upgrade install?
If upgrade you must do a clean install to work properly.
If you did a clean install. In an administrators account, type cmd in, search
In CMD mode type sfc /scannow. If you find errors and it is not fixed the first time do it several more times
If that does not succeed, boot form the windows DVD and chose repair install.
Get back to us either way.