Look in the management console (right-click My Computer, select Manage) and the logs (the application log, I think). It should have an error entry or two from mysql - that should tell you what the issue is.
I am running Windows 7, both 32-bit and 64-bit, on several computers and have MySQL installed and running just fine on all of them.
i am getting the same error while re-installing again !
I did not use Windows 7 but you can go to the User management link in the control panel and it will show your status.
But otherwise, if you are using the db for short periods of time then I suggest to use the zip version of the applicaton and you could run the db when ever you want...or better still get XAMPP, it comes with mysql bundled and a good system tray icon to manage the MySQL and other applications it bundles.