Avast is absolutely rubbish and a massive resource hog. It’s basically scare ware at this point, always trying to scare users into buying additional features.
Windows defender is great these days, I use it as my main antivirurs and do the occasional manual scan with malwarebytes.
I used Clorox wipes
Don’t do that again, those are not good for cleaning electrical equipment.
Most likely you just knocked something out of place. Reseat the RAM again, check all cables and clear CMOS.
So he says he’s not doing it, you block him and it doesn’t fix the issue, any chance maybe you are wrong and being a horrible housemate?
Perhaps there is another issue causing your speed issues and you are just taking it out on him.
WinDirStat is handy to find out what is taking up space and where. Also run disk cleanup.
The default option is to create an account but there is a sign in button aswell, seems you just clicked through without reading. IMO Samsung has the easiest UI for people that aren’t good with technology because it’s very basic.
You are about to find yourself in a whole lot less voice chats very soon.
If they are getting into accounts with 2fa then it would suggest your email is comprised or you have malware. Check your forwarding rules and reset email password. As others have suggested, scan your devices with multiple anti malware programs.
What makes you say you can only use 4gb? It’s showing that’s how much is currently in use and 15.9gb is available should it be needed.