Why did my computer suddenly go into slow motion?

I've got a core i7 6 core 3.33GHZ system with 24 GB of memory and a 2TB hybrid drive running windows 10. It runs well and is protected with Norton security, Malwarebytes, and superantispyware.
It's been running very well for at about 3 years. A few days ago they system went into slow motion.
It now takes forever to boot and when it does I can't really be productive. Naturally I ran all my security scans but they didn't change anything. However, when I unplug the ethernet cable the system returns to normal or at least close to normal.

Any ideas of what may be going on and how to resolve it?

Sounds like you've been hacked. Someone/thing is probably using your pc to send out millions of spam mails or worse.

I would spend a lot of time in windows explorer and look at files and folders to see if you can find some that don't belong.

And or plug in the ethernet cable and look in task manager for weird looking things that are running.

I figured I've been hacked . How they evaded my Norton firewall and antivirus and malwarbytes, and superanitspyware is deeply concerning.
I have looked into those files and folder but what is specious and doesn't belong is questionable. I'm considering reformatting and reinstalling windows 10. I'm not sure if there is any other way to be ride of this hacker.
What additional steps I can take to protect myself. Is Norton no longer up to task? Should I perhaps invest in a better router with firewall?

I would just uninstall SuperAntispyware. It hasn't been effective for a long time.

Did you check Task Manager to see what is using up resources? If it was running fine a few days ago, did you check Event Viewer? Did you install Windows Updates or make any other changes recently? If you have System Restore enabled, try a restore to an earlier point.

Some of these should prove worthwhile reading:

• Citizen Lab's "Security Planner" (Bruce Schneier advisor)
  
  
• Motherboard's comprehensive "Guide to Not Getting Hacked"
  
  
• EFF's "Surveillance Self-Defense"
  
  
• John Scott-Railton's "Digital Security Low Hanging Fruit"
  
  
• "Digital Security and Privacy for Human Rights Defenders"

As i mentioned in my other post it would seem the issues stems from a bad CPU. Basically your system shouldn't crash when running prime 95. down graded from 3.4GHZ to my original CPU 2.8GHZ and they system came roaring to life.

Yep. Continued here: http://www.sysopt.com/showthread.php...our-DVD-burner