No Taskbar, Start Button, Or Taskbar/start Menu Properties?

Yesterday, the task bar and Start button mysteriously disappeared.I've also found that the "Taskbar and Start Menu Properties" windowdoesn't come up. There are two places to click on in Control Panelthat should bring up this window, but it doesn't. The Control Panelborder changes color as if something is starting to happen, but thennothing happens, possibly indicating that some program starts to runbut then finds something wrong and exits. I didn't see anythinginteresting in the error logs. The desktop icons appear normally.The problem exists only when logging onto my son's account. When Ilog on as administrator, the task bar and Start button appearnormally.The usual tricks don't work: Ctrl+ESC, or bringing up Task Manager andtrying to rerun explorer.exe. I tried sfc to check for corruptedfiles, but none turned up. I ran an AVG scan and it did find one fileit considered a threat, which it removed, but that didn't solve theproblem.

I found a web site that referred to the registrykeyHKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionPoliciesExplorerwhich has a NoSetTaskbar value that can be used to disable the"Taskbar and Start Menu Properties" window. On the administratorlogin, the Explorer subkey is there all right, but doesn't haveNoSetTaskbar. (It does have NoDriveTypeAutoRun.) But when I log ontomy son's account, the Policies key had no subkeys at all. I triedadding an Explorer subkey without adding any values, but this didn'tsolve the problem. I haven't yet tried adding a NoDriveTypeAutoRunvalue, but since this seems to pertain to AutoPlay it didn't seemrelevant to this problem.Any thoughts as to what might be going on or what might fix it?