is this a clean install, in-place upgrade or factory install?
Uncheck everything in msconfig>startup except AV and gadgets.
Check the Event Viewer>Custom View>Admin log to google repeat errors to find how others have resolved them.
Install a lightweight free AV like MS security Essentials, which supplants Defender.
Run Driver Verifier to see if drivers are hanging: Using Driver Verifier to identify issues with Windows drivers for advanced users
Check the Performance log on Advanced Tools page accessed by clicking WEI score link at Computer>Properties. Look for cued issues at top of tools page, Generate A System Health Report.