when i go to folder option and tell to unhide all hidden files, and open the folder option again i find the settings is again in its default status.please help.......

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Curr entVersion\Explorer\Advanced\Folder\Hidden]

change the checked value to 2

or better import only this part of the registry from other computer

Are you setting this folder settings or system wide folder settings?

If you are experiencing system wide explorer not remembering folder preferences, this is a known issue and there is a fix.

I assume you are running XP, however Vista has a similar work around.
TweakXP.com - Fix Folder View Memory Loss