Hi there, I have exactly the same problem as ronnie.barker. !
I have only just udapted to Yosemite (10.10).
Before, I had turned spotlight off for ages because it slowed my time machine backup down.
Now I just wanted to test it and turn it on again, because the search in Mac Mail.app doesn't work - and I would need the search there now.
I tried the command
sudo mdutil -a -i off (and on)
and it came up with:
mdutil[1766:78805] Metadata.framework [Error]: mdsCopyStorePaths failed: (268435459) (ipc/send) invalid destination port
Spotlight server is disabled.
After that I tried the command Rodger also recommended (sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist)
and Terminal did not seem to react, the Spotlight Search still does not work or show that it is indexing - how can you check that it actually does?
After that I tried the command again and now it says:
/System/Library/LaunchDaemons/com.apple.metadata.mds.plist: Operation already in progress
Does that mean it is indexing now? How do I know how long it will take?
Thanks a lot for any help in advance!