If he can't open anything, I am betting he can't open malwarebytes?
When that happened to my computer (and I am not an expert here by any shot so my explanation might even be off) they had to somehow set my computer to make it think it was before when it was infected and then use malwarebytes plus another one (might have been glary utilities or something like that) to fix it.
I have an 11 year old son, so my heart is going out to you right now.
If you tell your dad, he probably is going to be mad because this is the reason he told you not to download anything and you didn't listen. That is the truth. Prepare for it.
But I think the best thing to do is "man up" and confess to him that you did not listen to him as you should have, and now you have a virus. Tell him that you were initially going to ignore it and hope it went away, but then you realized that was not the responsible thing to do. You realized the responsible thing to do was to admit your mistake and tell him.
Suggest to him that as a penalty for not listening to him, you will forfeit all of your screen time for a week and use it to do chores for him to help pay for the cost of repairs for the computer. Then agree that if you ever want to download anything in the future, you will ask his permission first, until such time you have a job and can pay to get it fixed yourself.
I know my son will make mistakes. All 11 year olds do. But I am much more forgiving when he takes responsibility for his own actions. In my opinion, that is your best course of action right now.
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Mom to 2 exceptional atypical kids
Long BAP lineage