If worse comes to worse you can always delete the .kde or .kde4 folder from your home directory, log out then log back in. The desktop will be reset to it’s original defaults. You will need to reconfigure the desktop to get it looking the way it did before.
If you right-click on the desktop and select “add widgets,” near the bottom of the list will be both “System Tray” and “Task Manager.” If they are not, try reloading them by using the “install new widgets” button at the bottom of the “add widgets” dialog box.
Actually I was not looking for “system tray” or “task manager”. I was trying to get my “panel” back. I had to delete my account and create that account again. Then I got my “panel” back.(I renamed my “home” folder to “home_old”. That way I saved what I wanted, but had to do a lot of settings again.) And after I logged into the new account, the “add panel” option is showing when I right click on the desktop.This was not there before. I remember I had a “Refresh desktop” option that is not there now…
Can anyone tell me from where to add or delete options which appear when we do a right click of mouse on desktop… I am just curious