What OS are you running?
Have you tried system restore? or....
Do you have access to the registry editor? (type "REGEDIT" into the run box)
if so then go to this key :
there you should see settings for windows explorer and the taskbar.. (a number "0" = setting disabled and a number "1" = setting enabled) just look for the settings related to the taskbar
the settings you are looking for are probably these:
REG_DWORD 0x00000000 (1) "
"NoTrayContextMenu REG_DWORD 0x00000000 (1)."
Just right click the setting and chose "modify" and change the "1" to a "0" or "delete" the key all together
(I am running windows 7 and all three subkeys under "policies" : EXPLORER , MOBILITY CENTER AND SYSTEM are all empty with no policies set)
better no policy then the wrong policy...lol
if you do not have access to registry then "system restore" option is best .. (if you have somehow edited the group policy preventing you from running system restore then try booting into safe mode and going to the Hidden Administrator account.. and running "system restore" from there... hopefully since that account is usually not used it will hopefully have all of the group policy settings still at their defaults and allow you to restore the system
NOTE: System restore is best option because it replaces the entire registry with a back up copy and all group policy settings are contained within the registry and will be fully restored back the way they were.
if system restore is unavailable then a manual restore operation can be done as a last resort as long as the system restore points have not been deleted... but that is a complicated process that requires putting your hard drive into another computer and manually moving the right files to the correct locations (definitely an expert task...lol).