I recently upgraded two PC's to Windows 10. The first one was on Windows 8.1, with both Mathematica and CDF Player installed as separate programs. The upgrade went well, no change in behaviour of either Mathematica or CDF Player.
Not so on the other PC. It was on Windows 7, with only CDF Player installed. After the upgrade CDF Player takes a painfully long time to start. 4~5 minutes until the Welcome Screen becomes accessible. This is what I see for most of that time:

Did the obvious: Reinstalled, played with the Compatibility settings in the shortcut. No improvement. Has anyone else seen this? And found a workaround?