Fs2004 switch task issue

hi
i was flying on fs2004 today and i found out that when ever i switch task to go to my desktop and then back into the game the plane would lose control and start stalling and turning..although whenever i task back into the game the plane tries to establish its self in means of what ive entered the FMC.
any suggestions why this occurs when i task into my desktop ?

p.s ive tried 737 pmdg as well as level d 767 , both with same result

any help would be appreciated

thanks
Tarek