Maybe you are running out of hard disk space so Windows has less virtual memory to work with, or maybe you do not have sufficient RAM or processor speed or a good enough graphics card to run Flight Sim effectively (I don't know the minimum specification for the game).
Jondoe is spot on, if you have trouble with Windows passwords you can search your computer for files that end in .pwl as these are the files that store all your windows passwords. They are usually found in the "c:\windows" directory of your hard disk. Simply delete them and your problem is solved.
Good luck. <img src="graemlins/dizzy.gif" border="0" alt="[dizzy]" />