Proxy Server Settings

I have a problem. I have changed something in my proxy server settings that causes the web broweser on the client machines to try and download the page instead of displaying it. It is using the application/x-msdownload mime interface to accoplish this. I don't know what i changed as i was also in the middle of a virus problem. Can anyone help me and suggest any fixes. I am hoping that the problem is with the proxy because it has affected every client machine. I thought at first it may have beenthe virus, but it was not. It may also be in my IIS server. I can go to the client machines and uncheck mark the settings in the web browsers configuration that cause it to use the proxy. As long as the proxy client software is installed the browsers will work. But i need to fix this problem. the message say "you are trying to download '/ from excite[2]' do you wish to save or open in its place. This happens with any web page that i try to go to.