When logging in with a new profile, there is no Panel.
You can right-click the desktop and Add Panel > Default Panel and then you have a panel. The default Panel is rather spartan though; just a menu, show desktop button, task manager, system tray, and clock. KDE4 would usually have some other launchers (Dolphin, systemsettings or mcc, maybe a browser), virtual desktop pager and lock/logout applet. Just something to think about.
*** This bug has been marked as a duplicate of bug 19148 ***