I have the above mentioned PC that has windows 10 pro installed. The issue:
Upon boot the PC stays on black screen for 5 minutes the shows login screen. After logging in the PC takes another 5 minutes on black screen before Windows 10 appears. After that the PC is wonderful.
Created a second user account. The PC actually boots fast to the login screen and fast into Windows 10, however everything seems to work great except the Windows 10 start button and cortana. I can right click on the button and use it, but not left click or use cortana. I can however click on file explorer etc just fine.
Ran chkdsk /f, sfc /scannow, uninstall/reinstall graphics driver, no malware found, edit registry runonce processes per google, windows updates, uninstall antivirus and restart windows explorer in task manager, disabled all all startup items, uninstalled all hp software. Checking event viewer now for errors.
Note: This doesn't seem to be the same as the familiar "taskbar doesn't work at all" problem. Just the start button.
Note: There are no windows 10 drivers on the HP website for this model so cannot upgrade bios. Has an HP Mobo.