You really think it's a windows issue like that
To be honest, without sitting in front of it and diagnosing it, I really don't know what it is based on the above (Not to say you're not explaining it properly, just an odd issue that requires some digging).
In my mind, I'm thinking Malware, but I've been wrong before. And based on your series of events that you've described, it could be any number of odd issues.
I suggested the above mentioned process simply because it is the best way to rule out anything software/driver related completely (less undocumented conflicts with that particular mobo/chip, however unlikely).
The conflict hypothesis is extremely unlikely, although not impossible, simply because your chip is processing some kind of instructions sent by some software program. A hardware conflict would produce blue screens or some kind of other failure, not idle usage.
Anyone else's opinion that's posted here is just as valid as mine because that is a very odd issue indeed given the history of events. If it were me, however, I would wipe it clean considering that you're not too far into an install to really lose much.
So in short; No, I don't believe it to be a Windows issue as described above, but considering the current state of install as described, you're not losing much time to [almost] completely rule out anything software related.