......... choose a lock screen picture you have not used before. You should see that in the Lock Screen when you lock your screen. Now, go back in and choose pictures at random, over and over again for a few minutes. It took a couple of days for some odd reason before full functionality returned, including previewing the past five choices, but that might just be because I did not have time to play around with it for a bit yesterday before full functionality returned after playing around with it today.
Well, this might fixed your problem but the resolution seems to be a matter of chance. Coz I tried every possible solution several times. At the end, yesterday, i decided to create new user. i will not describe the solution in details but hope everything will be clear enough.
If you have your current account linked with live accounts then turn on Sync your settings from Change PC Settings - OneDrive (former SkyDrive) - Sync Settings.
Then I disconnected Live account which led to creation of local account. (Change PC settings - Accounts - your account)
Then logged in as administrator and added new account with Live email address (Change PC settings - Accounts - Other accounts - Add an account)
Logged out from administrator account and logged in with new account. (you will still have local account available)
Because it is first time you log in to that accounts windows will take some time to set everything up. once everything is set you should see same start menu as you had before, thanks to the Sync settings option. However apps you purchased and downloaded from windows store will have to be installed again.
After that copied all my docs, pics, musics, and desktop files from local (old) account to new live account and deleted the local one.
By doing so I avoided to do system restore moreover this fixed problem with flash player not working for particular web sites.