Don replaced the power supply on his computer, but now it's having trouble seeing the hard drive he pulled out and plugged in using a drive dock. He got it working, but now he's having problems using Windows functions or downloading PDF files. All he did was replace the power supply and hard drive. Leo says it sounds like the installation of Windows 10 has gone bad. It may be a good idea to refresh Windows 10 or flat out reinstall it. It sounds like there are issues with hard drive permissions. So if the data is already backed up, start over. Reformat the drive and then reinstall Windows. If he doesn't want to do that, then he can always type Windows key + RECOVERY and repair it.