ITunes Match no longer working

Question

Wow. I don't even know where to start with this. But here's the problems I am having- I am hoping that someone can steer me in the right direction. I've been trying for a few weeks to get this straightened out and am still quite stuck.
I had iTunes match successfully running, with @35,000 tracks. But about a week ago I could no longer "see" anything that is in the cloud- my computer at work will only show the 12k songs on my hard drive.
Things to know:
1)I no longer have the cloud icon showing to the right of Music in the iTunes viewer window.
2) I've tried selecting Update iTunes Match. I've selected Turn Off iTunes Match, and then Turn On iTunes Match numerous times.
3) Checked to make sure iCloud Download and iCloud Status is enabled in the View Options.
4) iTunes Match shows up below iTunes Store, and it is stuck in that Start process. I can start it, it acts like it is going thru the process, then sends info to Apple, then goes back to the same view (iTunes Match, with the three steps and the Start button)
5) I've tried accessing my iTunes match songs from 3 different computers now, and I am getting the same results.
6) iTunes knows that I have more than 25k songs in the cloud because I get the nag screen New songs could not be uploaded because I've exceeded the 25k limit now. (In fact, that nag screen shows everytime I launch iTunes, even though I've toggled the box Do not show this message again)
7) On my computers, 99% of all of my songs now say Exceeded Limit in their iCloud Status collumn, even when they are songs bought thru the iTunes store.
8) I've tried reinstalling iTunes 10.5.2 a few times now.
9) Hide music not on this computer is not on. But for good measure, I've tried selecting it, and then reversing it just to see if that changes anything. It doesn't.
I'm totally at a loss here. Anyone been thru this before and figured out what I might need to do? I am highly frustrated that I currently can't find 2/3rd's of my music library.

Answer 1

An effective way to work with such a large library is to operate on the assumption that iTunes Match will fail to 'match' a significant proportion of the library.
Songs most likely to match are more recent Songs from iTunes or good quality CD rips (256 kbps).
From your symptoms it is worth starting afresh, hence:
1.  Start by restoring your original library with iTunes Match off from a secure backup;
2.  Create Smart Lists to segment your library into Songs recorded in c.5 year blocks;
3.  Export from each Smart List to a discrete directory for each 5 year block;
4.  Create a new library, import from the 1st 5 year block;
5.  Turn on iTunes Match and allow the 3-step process to complete;
6.  Create a Smart List for those Songs with an iCloud status of Matched;
7.  Save the contents of the Smart List to a discrete Matched Songs Directory;
8.  Delete the Matched Songs from the Library and the iCloud;
9.  Import the next 5 year block and repeat process from Step 5 until all Songs have Uploaded.
The result will be a library with all your Songs uploaded using the iTunes Match service and a set of directories containing all the Songs the you know will match.
At this stage the next step depends on the size of your library.  Given that you can only upload 25k Songs per library, with luck you should have a match rate that has allowed this.
Given that Matched songs do not add to this total you should now be able to import the Matched songs in 5 year blocks to the same library - allowing iTunes Match to complete for each set loaded until the full library is available.
If, however, you have hit the 25k Song limit - you should delete the last 5 year block to bring you back to a legal level.  Create a new library and complete the steps above for the Songs over the 25k limit on the new library.  This will give you two legal sized libraries with iTunes Match in successful operation.
Throughout, taking care to ensure secure backups are taken at each step is important to allow you to recover should iTunes Match at any stage have a problem - there are many potential pitfalls including file types that it may not like, interference from firewalls / antivirus software, corruption of files at source / in transmission.
The final result should be very good - though the 25k Song limit may frustrate you given the size of your current library.