Start button and task bar does not work

Open Notepad.

Copy-paste the following-

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon]
"Shell"="Explorer.exe"

[-HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\StuckRects2]
[-HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Streams]
[-HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\StreamsMRU]

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
"NoToolbarsOnTaskbar"=dword:00000000

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
"NoSetTaskbar"=dword:00000000

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
"NoSaveSettings"=dword:00000000

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
"NoActiveDesktop"=dword:00000000

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
"ClassicShell"=dword:00000000

[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Explorer Bars\{32683183-48a0-441b-a342-7c2a440a9478}]
@="Media Band"
"BarSize"=-


[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
"NoBandCustomize"=dword:00000000
"NoMovingBands"=dword:00000000
"NoCloseDragDropBands"=dword:00000000
"NoSaveSettings"=dword:00000000
"NoSetTaskbar"=dword:00000000
"NoToolbarsOnTaskbar"=dword:00000000

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Group Policy Objects\LocalUser\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
"NoMovingBands"=dword:00000000
"NoCloseDragDropBands"=dword:00000000
"**del.NoMovingBands"=" "

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
"NoSaveSettings"=dword:00000000

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Group Policy Objects\LocalUser\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
"NoSaveSettings"=dword:00000000

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Group Policy Objects\LocalUser\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
"**del.NoSaveSettings"=" "


and save the file with a .reg extension.

Exit and double-click the file.

Probably some trojan or DOS(Denial of service) tool has done this. Run a virus check if the problem persists even after running the reg file.