FS2004 is lagging just too much?

Hi,I run FS2004 as adminstrator but when I open it FS2004 starts quick and doesn't lag on the options or when it loads a flight. But when it finish loading a flight it takes 1 minute or 2 minutes maximum to be normal and when I press ALT for something it takes another 1 minute. I use the same settings in this youtube video http://www.youtube.com/watch?v=BXOdU7LJqgs.These are the addons I haveAerosoft HeathrowAerosoft Paris Charles De GaullesFSRecorderFsPassengersMy computer is a HP Pavilion Windows 7 Home Premium3GB RAM2.70GhzIs there anything wrong or any solution for this terrible lag on FS2004?Thank You