When you boot Windows, do you see your desktop background but no taskbar? Do you have to run explorer.exe manually to get back to normal? Here are some troubleshooting tips:
1.- First run a scan to make sure it’s not a virus or malware.
2.- Boot into safe mode. If things are normal there, it may be a program starting at bootup that’s causing the problem.
3.- In the registry editor, navigate to: HKLM \ SOFTWARE \ Microsoft \ Windows NT \ CurrentVersion \ Winlogon
4.- click Shell in the right pane and ensure the value is explorer.exe
5.- click AutoRestartShell in the right pane and ensure the value is 1 (hexadecimal)