If the Clock is missing from the Notification Area or Systray in Windows Vista, a registry entry may be the problem. First ensure that you have tried to, enable the clock. If that doesn’t work, try the following fix:

1. Hold down the Windows key and press R.

2. Type regedit and click OK.

3. Click the plus sign next to HKEY_LOCAL_MACHINE
then Software
then Microsoft
then Windows
then CurrentVersion
then Policies
then click Explorer

4. Look for an entry on the right side for HideClock. Right-click the entry and Delete it.

5. Click the plus sign next to HKEY_CURRENT_USER
then Software
then Microsoft
then Windows
then CurrentVersion
then Policies
then click Explorer

6. Look for an entry on the right side for HideClock. Right-click the entry and Delete it.

Now restart the computer and see if your clock is visible again in the Notification Area.