|If you installed MS SE, but did not uninstall AVG, then that is probably where your problem is. You cannot have more than one AV program installed at one time, there is a conflict.|
I always recommend running disk clean up before running defrag since many problems often are related to overstuffed temp folders and similar.
Whenever you are not sure your antivirus picked up on an infection, run Malwarebytes, it is compatible with antivirus programs and often helps.
Reducing the number of programs loading with windows often solves most slow start up problems. Manufacturers and software publishers always think you must have everything already started so you can easily get to everything immediately, but taken to the extreme, the opposite is the case. With everything starting with Windows, start up is slow and with everything in memory launching new programs and even the pre-launched programs just simply run slower making that new or relatively new machine fell like an old Windows ME machine. Run lean, run fast. start a program when you want it, shut it down when you are finished.
AS stated above, don't spend many hours figuring this out since a factory restore will fix nearly all software issues, but make sure you do a back up of your files first, and put together anything you installed since, and make sure you run only one AV program, and one software firewall (Windows one is best here).
You have to be a little bit crazy to keep you from going insane.