windows - How to monitor what triggers randomly starting program?

BACKGROUND INFO

Hi,
so the following has happened to me:
Suddenly I realize that the program on Windows 8.1 that was associated with .mp3 files randomly starts, sometimes multiple times per minute. At first I thought the app in question (think it was Xbox Music) was to blame, so uninstalled it. What happened then was that the windows chooser for "which app to associate with .mp3" started to pop up with the same randomness and also sometimes multiple times per minute.

Next step I did some virus search, using (not at the same time) Windows Defender, Avast, Avira, BitDefender. So it seemed like some cryptocoin mining software that I don't use was infected (no problem, no coins mined), so I let the virus program move all those files to quarantine. Some android root software also got marked as virus, although i suspect there were no harm in those files.

Now, virus softwares reports no error, but .mp3-program is still triggered. I didn't want to troubleshoot anymore, so decided it was time for a clean win install. This all happened while connected to my college LAN, wired connection (writing a thesis at the moment).

I stayed at home next day reinstalling windows and other stuff, seems nice and everything. When I got to college today, and connecting wired again, and in a few minutes the music player starts multiple times. Note: if the software allows multiple instances, like VLC, there will be multiple instances!

While doing the reinstall, I had quite a lot of personal files that needed to be copied back on the new win install,so that is a possible source of viruses. However, i cannot help suspect that someting on the college lan triggers this, especially since i don't remember the music player starting at home. Actually, it is now windows media player and i got the "configuration wizard" when it first started this morning at college--> first start of wmp --> did not start earlier. I naturally have internet at home.

SETUP

Windows 8.1 x64 all windows updates installed, windows defender running.

QUESTIONS

-How to monitor what triggers random starts of software associated with .mp3 files? There is never any file to be played, just the program that associates with .mp3.

-Other suggestions: virus softwares, should i contact college IT department, etc?