I just threw out the suggestion as a long shot, 'cause you sometimes find answers in unexpected places. With a single machine experiencing the problem, and no obvious solutions, it was worth a look. I'm sorry, but I just can't see an obvious hardware issue; and that includes power saving settings for the adapter and the like. So, that doesn't leave much except malware or a Windows installation that's so messed up that you need a drive wipe and reload. After all, you've experienced the same problem with two network adapters, so I can't see how hardware is a factor. My experience is that power saver settings for network adapters are very, very seldom the root cause for connection issues. Doing a repair installation of Windows can leave a multitude of problems unresolved.