Are you able to contact the company that provided the Mac and set it up for you, if you are it may save a lot of time and frustration for you.
However if that is not an option we need to know what update the system performed was. Look in the App Store under the Updates menu, it gives "updates installed during the last 30 days".
I am presuming you accessed Win 7 through Parrallels.
Use Spotlight to search for Parrallels, that may show where it as hidden itself.
The more info you can provide ( don't show any personal info though) may allow somne one on the forum to get you working again.