My pc slows down my wifi download speed.

My pc slows down my wifi download speed. I have a router with a quick 5g ethernet that gives me 300 mb/s download speed and it was always like this. Recently I gave away my pc and my keyboard to be cleaned from all the dust it has collected over the years. And maybe i'm wrong but i think since then the problem has occurred? My pc works alright, it doesn't make any weird sounds or anything. However when i download a game the internet speed is just horrible, not only that, when i was downloading an update on steam to Space Marine 2 my disc seems to work faulty as well. While steam was using 100% of my disc the download speed was only 7 or so mb/s... even weirder my disc temp. seems to be stable and non concerning... It's worth mentioning that I also have an xbox, and on my xbox the internet speed seems to be just fine at ~300 mb/s, downloading a 60 gbs update in half an hour, while on pc i have to wait the whole day. So could be the issue? Is it an error from the guys cleaning my pc(it might be worth adding that they also changed my processor paste), maybe it's a faulty ethernet cable but that doesn't explain why my disc is going crazy while patching in a steam game update.

This is my first time asking anything about pcs i don't know anything really about pcs