I have recently begun experiencing this problem after updating to Windows 8.1 (although I'm not sure that it's directly related to the update). I see that similar questions have been asked on other forums, but I see none for 8.1.
The best way to describe the problem is this: while using a particular window (such as a browser window or word processor window), the window will randomly become inactive. Sometimes it will switch back to being active automatically, other times I have to manually click back into the window to use it again. This is especially frustrating when trying to type or use drop-down menus. As I type this question I am constantly clicking back into the browser window to keep it active. The problem appears not to be specific to any particular program or internet browser, but occurs for any window that I happen to be using.
I don't know if this is relevant, but the activity of one particular background process appears to correlate with the timing of the problem. The process, "HPConnectedRemoteService", is continually appearing and disappearing from the Task Manager. It appears, increases gradually to about 20% CPU, then disappears. Any given active window will become inactive when "HPConnectedRemoteService" reaches about 20% CPU. Again, I do not know for sure if this process is involved with the problem though. Attached are several screenshots of the processes running, in case they can aid in solving this.
Would really appreciate any help! This is incredibly annoying and counterproductive!