After being on the phone with Xbox Customer Support for 90 minutes and getting disconnected, I decided to try my hand here. During my network test, everything checks out ok (open NAT and everything), but I can't sign in with my Gamertag. The customer service rep then asked me to make a free 1-month account to see if that would sign on to Xbox Live, and it worked just fine.
My account is not suspended, and this started happening after I downloaded the latest system update. For some reason, I cannot recover the Gamertag or anything.
I don't want to lose the account. I'd hate having to restart my Gamerscore, I have a bunch of Microsoft Points left on my account and have bought a lot of things. I don't want to lose any of it.
Hopefully I'm being specific enough, but if not just ask if you're confused about anything and I'll try to clear things up.