1 PC is slowing down the whole network?

Ok please help so my computer is slowing down the whole network. The pc its self is getting really slow and bad wifi connection, on steam im geting roughly 100 KB/s and that keeps dropping out? My laptop is currently getting 1mb/s
Iv done a total reinstall of windows 7, it was running as should be for 2 days and then went back to being painfully slow again. Iv changed my anti virus from avast to AVG neither are picking anything up. Iv not even done much web browsing on it since the total reinstall, nor have i downloaded anything (exept firefox, anti virus Ccleaner etc….. )
I really cant figure out what is going wrong, if anyone has any ideas id be really grateful, thanks.
Answer #1
wifi connection problems maybe related to receiver on your pc since you get better speeds with laptop which shows there is no problem with the signal.
if you just formatted your pc and did a fresh install , also you are sure about that you didnt install anything bad yet pc was slow even just after the reinstall , the first thing to check is harddrive.
https://www.piriform.com/speccy/builds
download “portable” version on this page , after extracting just run it. on the left pane of the software you will see “storage” , go there and find your harddrive among the listed , check its SMART value , does it say good or critical ?