A common reason your search indexing is not working is a Registry Error. One of the Search Registry Keys points to a directory that does not exist. None of the common solutions, including the Windows Troubleshooter, fix this problem. Many different error messages may result.
The solution is to manually check two keys in the registry. Check these keys:
Registry Location:
Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Search\Gathering Manager\
Default Keys:
DefaultApplicationsPath = %ProgramData%\Microsoft\Search\Data\Applications\
TempPath = %ProgramData%\Microsoft\Search\Data\Temp\usgthrsvc
Make sure these two keys point to valid directories. Otherwise, create the directories. Do not change Registry Keys unless you know what you are doing. Creating directories is safe. Changing Registry Keys is not.