Well, I found it. The information is the following:
aspnet_wp.exe could not be started. HRESULT for the failure: 80004005
aspnet_wp.exe could not be launched because the username and/or password supplied in the processModel section of the config file are invalid.

I was using WEB Matrix. I installed it the other day. Don't remember, if it asked anything regarding login and password.

What should I do now and how can I change it in config file?

>I'm trying to run ASP page, which worked fine on Friday.
>
>I'm getting this text in the Browser now:
>============================================
>Server Application Unavailable
>The web application you are attempting to access on this web server is currently unavailable. Please hit the "Refresh" button in your web browser to retry your request.
>
>Administrator Note: An error message detailing the cause of this specific request failure can be found in the system event log of the web server. Please review this log entry to discover what caused this error to occur.
>================================
>How can I review the Server event log?
>
>Thanks in advance.