Alright so I got it working! I basically followed all of the advice offered since my last post in one go (probably not a good idea in general), rebooted, and manually ran GWX.exe under...

Yup, I'm totally up to date except for a couple device drivers that I've hidden. The Update settings are set to "Install updates automatically" with every box below it ticked.

Hmm, is there any list or anything of what software is incompatible? As far as I know I don't have anything out of the ordinary installed.

I definitely meet the minimum requirements: i5 2500k, GTX760, 8GB of RAM, and a couple TB of storage across multiple drives. I have all my drivers and whatnot so there shouldn't be any issue...

I turned Avast off last night, rebooted without it running all day today and still nothing. Any other ideas?

I'm having the same issue on my Windows 7 x64 PC that is fully activated with a retail key. The update in question (KB3035583) installed as usual about a week ago, but the notification never showed...