If you have set your power plan to Balanced, that is normal for the processor clock speed to increase and decrease depending on what actions you are performing.
To rule out system corruption as the cause of the system crashes, open the Settings App.
Go to System - Recovery.
Click the 'Reinstall Now' button in the 'Fix problems with Windows Updates' section and wait for that process to complete.
This process should fix any corruption in Windows and will not affect your files, settings or installed apps.