The DMCA should not pertain to you flipping bits into your own copy of Windows to modify it's functionality. You can do that, and if it's a violation of the license, Microsoft can sue you. It's an entirely civil issue with the burden of proof on MS.
The anticircumvention provisions of the DMCA criminalize any alteration of a device with the purported objective of protecting copyright. So now the state not only defends copyright, but the technical measures themselves, even if the real objective of the manufacturer is simply to be anticompetitive and incompatible. It's a massive privatization of criminal law in ad-hoc, unwritten form: "it's illegal to disable anything manufacturers claim defends copyright".
Wrong. What defines owning is not whether you paid or not, but the type of contract you made.
Moreover, you didn't pay for Windows; you paid for a license of Windows. This license specifically says what you are and what you are not allowed to do with the software, and among others, tinkering with is is not part of what you are allowed to do.
I mean, there is obviously a law stating that you cannot do this or that because it violates copyright. This implies that you as a citizen might do something illegal as close yourself in your room, do some magic and then get out and forget about it, although what you did has no influence on the world whatsoever. That is a problem.
Now, if we want to be precise there is actually a clear definition of what you own, and in fact you probably do not own the copy of Windows running on your PC. Still it is possible that you own that PC, and its hard drives and other stuff, so when we say that you do not own the software but just a license to use it we are giving credit to stuff like this:
http://www.makeuseof.com/tag/10-ridiculous-eula-clauses-agre...
or this:
http://www.zdnet.com/article/apples-eula-nonsense/#!
To sum up, sure you might not have the right to hack your properties, but that's caused by a set of laws defending a power inbalance between consumers and producers. I believe that claiming that any sort of "hacking your stuff" should be prohibited because the law says so is an example of irrational justificationism if not supported by further arguments, still I'd like to hear about the reasons why we need copyright law as is.
Those EULA are dumb, but you don't have to agree with them. In many cases there will be no alternative, for sure. However you can't accept an EULA and subsequently say "this EULA sucks, I don't have to follow it".
I never met a human (excluding lawyers) who actually has read through a single EULA, and I doubt most of them would be valid if actually tested in court, at least outside the US.
[edit: typo]
Edit: Often it's not even at purchase. There are numerous apps that will do this every time they change their terms. And they don't show you a change list either. It's the whole 50-150 pages. No reasonable person would actually read it.
It'd be great if anyone could point to interesting resources on this issue. It seems to be an intriguing intersection of law and economics.