In that case, no, Microsoft would not be able to do anything to someone who found a Windows DVD modified to remove the EULA check:
1. Copyright would not be involved because copyright cover the reproduction and distribution of content. You did neither. It'd be the same if someone photocopied a book and you found the copy on the ground. You might argue that "well, you need to copy the software from the DVD to the system". If that's a problem, imagine that the mysterious individual also somehow installed the OS on your computer without your knowledge.
2. Patent law doesn't apply because patents (in theory) cover the application of techniques and technologies. Patents are irrelevant to end-users.
3. As stated before, the EULA also doesn't apply.
IMO, applying patents to living organisms is completely bogus, conceptually. It'd make more sense if the genetic information of the organism was copyrighted. Then it would make some sense to talk about unlicensed copies being made, although it'd still be rather tenuous. Copyright wasn't thought for self-replicating and randomly-modifying data. Has a law been broken if a disc undergoes mitosis? How many words would you need to change for a book to no longer be considered the same?
What's about all these comparisons with software in this thread ? It's completely irrelevant. Crops are used for people to eat, it's their means of survival. Microsoft can do what they want, it's still software, there is no comparison possible.
We should not be able patent/copyright seeds at all for obvious reasons, it's what people use to survive every day... And if that means that Monsanto will die and the research should be made public, then I'm all for it. No company should have that kind of power at all.
PC-Company-A signs no license with Microsoft. An employee of theirs finds a copy of Microsoft Windows laying on the ground.
Having no agreement with MSFT, and having discovered Windows "on the wind", as it were, they start to install it on their PCs.
Is it Microsoft's business? PC-Company-A has no license with them, why should it matter?