when i first boot up my PC i see a black CMD box for like 0.3 of a second, is that malware?
I forgot to answer this.

Not necessarily. Any console program or batch file can produce this. Usually, a developer will try to hide any console from appearing so as to not scare you like that, but sometimes more simple programs or batch files that run at startup don't do this for some reason. I see them as well.

Malware could do this, but it's something you will often see with installers. Occasionally just startup programs can do it, especially if programs are "checking for updates" upon running.