I have a Dell Axim X51v and a desktop running Vista Ultimate. It
seemed that randomly my Dell would stop synchronizing with WMDC. There
was no rhyme or reason. One hour it would work, another hour it would
just stop. It would work for a couple of weeks fine, then Boom! I
tried everything to get it to work. Uninstall the device, uninstall
WMDC, reinstall WMDC, reconnect the device, etc. I could verify that
the computer was detecting the PDA through Device Manager. I tried
everything to get it syncing again. There are a couple of long posts
on this forum that I authored looking for a solution. I eventually
bought a Bluetooth dongle and connected over BT to avoid the whole USB
to PC sync issue. But that was spotty at best. Well I've finally found
the solution.

The issue is with Dell's Notification Management update. Or more to
the point, my use of the Notification Manager. Dell's website mentions
the fix is supposed to be used to delete duplicate notification
entries to improve the PDA's performance. However Dell provides little
documentation for the application. Like me, you may think all these
things are just notifications and therefore harmless to delete. But
that is not so. If you run this app and delete the wrong one you can
end up killing your Activesync connection. I must have inadvertently
been deleting some useful "notification" in an effort to do
housekeeping on my PDA.

The other solution I found was a pretty useful app from SPBsoftware,
spbbackup. This application will let you back up your entire PDA, save
the executable backup file to an SD or CF card, and then run it to
restore all programs, data, settings, etc. To use it, I did a hard
reset and completely wiped my PDA. I then spent half the day
reinstalling all the programs, settings, wallpaper, themes, etc. I
then did a backup so I would have a place to restore from.

When I accidentally deleted some important notifications and
Activesync stopped working, I used the backup to restore, and
everything came right back.

Does MS still have some work to do with WMDC/ Activesync and
Bluetooth? You better believe it, but having a good backup and
watching your notifications may help if you're in the same situation
as I was.