Why is my computer so damn slow?

I mean yesterday it was working fine but after my little brother started playing this game called, "Bobba Hotel" (or something close to that name) which is a "retro" for a game called Hobba hotel. I did an Avg scan and also another scan with avast, it says nothing is infected. I did however,... show more I mean yesterday it was working fine but after my little brother started playing this game called, "Bobba Hotel" (or something close to that name) which is a "retro" for a game called Hobba hotel. I did an Avg scan and also another scan with avast, it says nothing is infected. I did however, remove like 60 tracking cookies. The Virus Chest had 4 sections, Infected files, User files, System files and All chest files. Everything is empty besides the system files. It has 4 "lines".

kernel32.dll

another kernel32.dll

winsock.dll

wsock.dll

I scan them and it says no virus. I am done with this. My laptop has been trough hell ever since we played games like Half Life 2 and cs:s

So please I just want to get this over with. I was gonna try system restore and see if that works.

Any ideas?
Update: Yes I cleared private data basically deleting cookies, history, etc. And no he can't download it browser based and I was so stupid since it said something about a security flaw and I was so busy going somewhere with my friends I didn't care.
Update 2: The startup takes so long but after my computer loads for a while it starts running faster but is still slow. My cpu usage is way higher than normal. I know something is wrong here. I'm gonna try some of these answers right now.
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