|Are you using a Mandatory Profile or an application like Deep Freeze on your PC's?|
I ask because you said, " i switch off these computer n on again,these applications get lost." and that to means you have the workstations locked down.
Just for a simple test, on any of the aforementioned workstations, what happens if you change the wallpaper on the desktop and reboot. After the reboot, is the original wallpaper back, or is the newly selected one showing?