Smart phone can't sync suddenly after two years

I went to sync my smart phone to my PC last night and windows tells me the
USB device I just inserted is not recognizable. I tried the other USB
ports - no luck. In Active Sync the phone is greyed out.
How can I diagnose the problem? Both PC and phone were shut down and
restarted but this did not solve the problem.

 

Have you tried a different USB cord. It may be possible that a windows
update caused the problem and you may have to reinstall some software that
you got with the phone.

www.windowsvistatips.com is a waste of time

 

I never bought another cord for the phone since it stays permanently
attached to my PC, so unlikely to get lost.
Over the weekend I bought a Bluetooth dongle and got errors trying to sync
from that also.
However I noticed that Outlook was working faster than it has been so tried
the USB cord again and this time it synced OK.

So maybe Outlook was causing it to fail reading the contacts, and that issue
has resolved itself (miraculously seeing as I changed nothing in Outlook!)
I can't use the SW that came with the phone since I upgraded the OS as soon
as I got it.