Hi win10needswork,
I’m Rey, your Windows 10 Advisor.
I understand you are having a CPU usage 100% when you did an upgrade from Windows 7 to Windows 10.
I had experienced this before and fix it temporarily but I was ended to do a clean installation.
The reasons why, since there will be several issues especially hardware configuration are designed original base from the Windows 7 system.
YOu may disable things but it's totally different if you'll do a clean installation instead.
Solutions to Fix the High CPU Usage
Solution 1: Restart the WMI Provider Host
Step 1: Search for Services and open it.
Step 2: In the window, find Application Management and right-click it. Then select Restart.
Solution 2: End the Processes that Cause High CPU Usage
Step 1: Search for Task Manager and open it.
Step 2: Click the CPU column header to sort the processes by CPU usage and check which processes cause your CPU to become higher.
Step 3: Right-click the process that consumes lots of your CPU and then you should click End task to finish this process.
Solution 3: Disable Third-Party Antivirus Software or Run an Antivirus Scan
Solution 4: Reset Your Power Plan
Step 1: Choose Hardware and Sound after you launch Control Panel, and click Power Options.
Step 2: Then choose Balanced if your computer is on Power saver.
Step 3: Then click Change plan settings that are next to the Balanced.
Step 4: Now, you just need to click Restore default settings for this plan and click OK to make the changes.
Solution 5: Modify Settings in Registry Editor
Step 1: Press the Windows logo key and the R key at the same time to open the Run dialog.
Step 2: Type Regedit and then press Enter to open Registry Editor. You’ll be prompted for permission and please click Yes to open it.>
Step 3: Follow the path to locate the correct system files: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TokenBroker.
Step 4: Right-click the Start entry on the right side of the pane and select Modify…..
Step 5: Then change the Value data to 4 and click OK to save the change.
Solution 6: Turn Windows Notification Settings Off
Step 1: You should click the Start button and click Settings to open the Windows Setting.
Step 2: Then choose System and click Notifications & actions on the left side of the pane.
Step 3: At last, you just need to turn off the feature Get notifications from apps and other senders.
I hope this information gives you the support you need. If you need more, let me know.
I believe that these steps will help you solve this issue you have. If not, kindly contact me and let me know.