Start > (right click blank area) Properties > Start Menu (tab) > Customize... > Advanced (tab) > Start menu items: System Administrative Tools > check
Display on the All Programs Menu > OK.
Start > All Programs > Administrative Tools > Event Viewer ......... Look at the entries under
Application and
System. If it's full of persistant Warnings and Errors, double click them for further info.
Take a particular look for event id entries 1517 and 1524; if you've got them take a look at
THIS and download.
If nothing of note is showing in Event Viewer, probably best come back here to pursue other options.