I may be way out of line here and if so I apologize. I am posting this question here because this group might be the only one savvy enough to figure this out. I installed El Capitan on 11.28.15. Everything seemed to be ok except updates from the App Store. When I click on "Update All", or even "Update" any individual, it acts like it is going to work and shows a progress bar like it's downloading, but after a few seconds it just stops and the update button goes back to it's unclicked "non-grayed out" appearance. I did download and install the full installation of 10.11.2 from the "featured" section, which worked fine, but updates still won't work. One thing I should mention is my soon-to-be ex wife did monkey around in keychain trying to remove her passwords. I don't know if maybe she deleted something pertinent? I would appreciate any advice.
While I do agree with @SGill there may be some small lesson here for the community. Like, "Messing with the keychain" is generally a bad idea, though I can understand why she'd want to. In any event, I would certainly try to visit an Apple store regardless of what you find online (even here). These sorts of things can go from super simple to, extra tricky real quick and if you don't have to know how to figure out which is which you'll end up in far worse trouble.
I will give you one decent and simple piece of advice. You should be able to greatly narrow down the issues by creating another user account (under Users and Groups within System Preferences). If this works then the issue is simply within the user account and not the "system" so to speak. If so, I'd recommend moving to a new user. Now this is a short and overly broad recommendation and I'll keep it that way. I wish you the very best!