It's caused by a context menu extension being installed.
I did a survey a few months ago of people posting here with this problem.
Unfortunately it seems many extensions cause this.
MS inbuilt ones don't cause this. One I know of that does do it is AVG AV
program. AVG said they are working on a fix.
The survey didn't turn up the names of other programs as noone had anything
in common.
Type regedit in Start Run
Navigate to
HKEY_CLASSES_ROOT\AllFilesystemObjects\shellex\ContextMenuHandlers
(only sendto is under here by default)
HKEY_CLASSES_ROOT\Folder\shellex\ContextMenuHandlers
(none here by default)
HKEY_CLASSES_ROOT\Directory\shellex\ContextMenuHandlers
(Encryption, offline files, and Sharing is under here by default)
There are two forms
<human readable name>=CLSID
CLSID=<Optional human readable name>
If you have any you can't tell what it is by the human readable name. Make a
note of the number (sharing is {f81e9010-6ea4-11ce-a7ff-00aa003ca9f6} -
we'll use that as an example) and look it up here
HKEY_CLASSES_ROOT\CLSID\{f81e9010-6ea4-11ce-a7ff-00aa003ca9f6}
Then find a server subkey key (most likely an InProcServer32 key but there
are other types). This will tell you the file it is in. Find the file and
view it's properties to find what program it came from.
To fix. Export the keys (right click the key - export) then delete each non
standard entry one by one till Start starts working. There may be more than
one that causes it.
It would be helpful to others if you post back the guilty ones.