Desired gamertag is taken, but not in use

There's no way to see what other services the tag is being used on i'm afraid.

If it isn't being used at all then it's anyones guess as to when or if it will be made available again.

Last time Microsoft released some gamertags a lot where snapped up by people who were then selling them on,which is against the rules.

Keep in mind that Gamertags are not strictly used for Xbox 360 but can also be used solely for Zune, Games for Windows, or Windows 8 Microsoft account. So just because the Gamertag doesn't show 360 activity it might actually be in use. There is occasionally a purge of completely inactive but there is no schedule as to when it is done.  So if you really want to use that Gamertag just continue to periodically check it for availability.

Great answers but just thought I'd add the Official Microsoft response to this question from this link:

forums.xbox.com/.../153151.aspx

I can't change my Gamertag (GT).

Most of the time if you are seeing a message saying the GT you want is unavailable, it’s true. One thing to remember is that spaces and capitalization don’t make your GT unique. For example, “Major Nelson”, “MajorNelson”, and “MaJoRnElSoN” are all the same GT.

GTs are also tied to services like Zune or Games for Windows LIVE. If a GT doesn't exist on Xbox, it might be in use on one of those services. If you try sending the GT you want a friend request and it says it’s not a valid GT that just means it isn’t used on Xbox LIVE, but it could be used for Zune or GFWL.

I heard old GTs are being re-added. When will "This GT" be available?

There is no schedule or estimated dates for when certain GTs will become available again. GTs are not an on-demand service. They will be available when they are available.

I Want a gamertag that isn't taken but it says it is?

[quote user="vL dFuze"]I Want a gamertag that isn't taken but it says it is?[/quote]

Just because you can't find it doesn't mean it isn't taken. Have you searched for all possible combinations of letters and spaces? For example, I wouldn't be able to find vLdFuze (no space), but I would be told that it already exists if I tried to change to it (because you have the version with one space). You might as well tell us what it is; somebody might be able to point out the profile you couldn't find.  

I'm having the same problem, I'd like to change my gamertag to "Sanojj" The account has been innactive since 2008 on xbox. And besides xbox i can't seem to find any other services that specific GT is being used.

Doesn't matter how long it has been inactive

Gammertags are not an on-demand serviceit is free when it is free just be more like creative