do you have access to the server itself?
assuming you do?
1) check the services in services.msc are running for the world wide web service
2) check the service for the database is running (depends what you use, sql or other)
2a) check local firewall settings on that server in case someone/something is blocking 80 or 443
3) assuming those are running, launch the browser on that server itself and see if you can connect there
3a) you could try http://lanssweeperserver/lansweeper.ico that should simply bring up an icon (if that does then the web server is running might be an issue serving the aspx or its content from there.