Eu finalmente resolvi o problema executando o seguinte script vbs. Ele faz algumas modificações no registro do Windows. Embora tenha sido originalmente projetado para o Windows XP, felizmente ele também funciona no Windows 7, pelo menos no meu caso. Minha barra de tarefas voltou agora, mas ainda não faço ideia do que realmente causa esse problema.
'xp_taskbar_desktop_fixall.vbs - Repairs the Taskbar when minimized programs don't show.
'?Kelly Theriot and Doug Knox - 8/22/2003
Set WSHShell = WScript.CreateObject("WScript.Shell")
Message = "To work correctly, the script will close" & vbCR
Message = Message & "and restart the Windows Explorer shell." & vbCR
Message = Message & "This will not harm your system." & vbCR & vbCR
Message = Message & "Continue?"
X = MsgBox(Message, vbYesNo, "Notice")
If X = 6 Then
On Error Resume Next
WshShell.RegDelete "HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\StuckRects2\"
WshShell.RegDelete "HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\StreamMRU\"
WshShell.RegDelete "HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\Streams\Desktop\"
WshShell.RegDelete "HKCU\Software\Microsoft\Internet Explorer\Explorer Bars\{32683183-48a0-441b-a342-7c2a440a9478}\BarSize"
P1 = "HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer\"
WshShell.RegWrite p1 & "NoBandCustomize", 0, "REG_DWORD"
WshShell.RegWrite p1 & "NoMovingBands", 0, "REG_DWORD"
WshShell.RegWrite p1 & "NoCloseDragDropBands", 0, "REG_DWORD"
WshShell.RegWrite p1 & "NoSetTaskbar", 0, "REG_DWORD"
WshShell.RegWrite p1 & "NoToolbarsOnTaskbar", 0, "REG_DWORD"
WshShell.RegWrite p1 & "NoSaveSettings",0,"REG_DWORD"
WshShell.RegWrite p1 & "NoToolbarsOnTaskbar", 0, "REG_DWORD"
WshShell.RegWrite p1 & "NoSetTaskbar",0,"REG_DWORD"
WshShell.RegWrite p1 & "NoActiveDesktop",0,"REG_DWORD"
WshShell.RegWrite p1 & "ClassicShell",0,"REG_DWORD"
p1 = "HKCU\Software\Microsoft\Windows\CurrentVersion\Group Policy Objects\LocalUser\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer\"
WshShell.RegWrite p1 & "NoCloseDragDropBands", 0, "REG_DWORD"
WshShell.RegDelete p1 & "NoMovingBands"
p1 = "HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\Shell"
WshShell.RegWrite p1, "explorer.exe", "REG_SZ"
p1 = "HKCU\Software\Microsoft\Internet Explorer\Explorer Bars\{32683183-48a0-441b-a342-7c2a440a9478}\"
WshShell.RegDelete p1 & "BarSize"
WshShell.RegWrite p1, "Media Band", "REG_SZ"
On Error Goto 0
For Each Process in GetObject("winmgmts:"). _
ExecQuery ("select * from Win32_Process where name='explorer.exe'")
Process.terminate(0)
Next
MsgBox "Finished." & vbcr & vbcr & "?Kelly Theriot and Doug Knox", 4096, "Done"
Else
MsgBox "No changes were made to your system." & vbcr & vbcr & "?Kelly Theriot and Doug Knox", 4096, "User Cancelled"
End If
O script também pode ser baixado nesta página:
Basta clicar em "Taskbar is Missing".
Boa sorte.