Are you running Windows or Mac, Tress08?
Assuming you are on Windows, close out of your Internet browsers first.
Next, press Ctrl + Alt + Delete together to open up Task Manager. Click on the Process tab, scroll down until you find gplayer.exe, then end the process.
You should be able to continue your Flash Player installation from there
Try it out and let us know how it goes.
More info on gplayer.exe: http://www.processlibrary.com/directory/files/gplayer/407826/