RockinRio is right on with the MSCONFIG link. Focus on the "startup" and "services" tab. If you mess with "services" startup, make sure you check the box that says "hide all Microsoft services". Typically when I troubleshoot this type of thing I disable all startup items and all non-Microsoft services. If the problem goes away, I enable all services, reboot, see if it comes back. This will tell you if it is a startup item, a service, or neither.
I bascally test with groups of the services and items to narrow it down (not one at a time). Once I narrow it down to 3 or 4 items, I test individually.
You can also scan for malware. I recommend the free tool at Malwarebytes.org
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Hope that helps!