Thanks for reply
I will try soft reset(Settings -> Privacy -> Restore Factory Defaults? )but i can't backup contacts it is hidden in kies..
Yes thats how you perform a Soft Reset.
As for Backup use Google Backup. Export your contacts to SDCard and the Import them back into Google Account.
I have 2 Q:
What is difference between hard and soft reset?
A Hard Reset is where do a Reset from an Alternative Menu or Key Combination.
A soft Reset is where you Initiate the Reset through the System or normal Menus.
The Difference here is for some reason the Soft Reset does a better job at doing the reset unlike the Hard Reset it's usually the other way round. A Reset basically restores Factory Setting sort of like how you got it new from the box. This doesn't however clear the cotents in your SD Card.
And i asked about download and recovery modes...is it necessary to have rooted phone to enter these modes?
No Root is a Privilege, rooted means having access to that privilege to change System files from within normal means.
Download Mode and Recovery Mode have nothing to do with being rooted or not, if you can't enter Download mode it maybe because it is disabled but you should still be able to Enter Recovery Mode