Wifi and internet slow only when my computer is on?

Beovy · July 4, 2017

Three weeks ago I went to a LAN so I brought my entire computer. When I came back from it, I left all my stuff sitting downstairs because I was too lazy to set everything up again. Yesterday, I decided to finally set it back up. Everything seemed fine, except for the Ethernet port. At the back of the IO, there was no flashing light when the cable was plugged in, and I was getting no internet to my computer. I restarted my computer, the modem, and the router (which is what my computer is connected to) several times but still no light. I tried a a different cable, one that was connected directly to the modem, and still no light. Finally, I tried a third cable, which I took from another computer from my house that I knew worked, and this one finally worked after plugging it in and restarting my computer. This cable is also connected to the modem directly and is what I'm using to access the internet right now. Finally having internet, I hopped into a game of League with my buddies and into their discord server. In game, my ping was at a solid 31, FPS was capped at 60 as always, however, I felt some weird lag. Here is a clip from one of the games I played: http://plays.tv/video/595bf95b313eb62fb4/lag

Stuff like this happened several times every game where particles wouldn't be seen, or the game wouldn't register my inputs until moments later. Everyone's voice in the discord server I was in was also very choppy. These problems would be even worse if I had a youtube video playing in the background, or even a simple webpage open.

There was another problem that occurred after setting up my computer. The wifi began to be very sluggish on the mobile devices connected to it. It remained on and connected the entire time, however notifications would only pop up every so often and sometimes things just wouldn't load at all even though it said it was still connected. I ignored all these problems for the duration of the day and kind of just bared through it. After calling it a night and turning off my computer, everything went back to normal...The wifi was perfect again. Today, after coming home from work I went to turn on and use my computer again, and the wifi became sluggish again.

Any ideas? My computer is almost 6 years old so maybe the ethernet port and IO has something to do with it? Taking too much bandwidth?

My router is the Asus RT-AC87U. We got it last year and it's been great. Zero problems.

The modem we're using is an ARRIS modem provided by our ISP. This also hasn't given us any problems in the past.

My provider is Cogeco. We have cable internet with ~70 down ~15 up

Just.Oblivious · July 4, 2017

Could be a background service causing a lot of unwanted traffic (like Windows trying to contact a machine from the previous network, or perhaps a piece of malware that made your machine part of a botnet).

Finding the cause of this problem requires a bit more investigation.

Here are a few things that you can try (in no particular order):

Download and install the latest driver from your network card chipset manufacturer (Realtek, Broadcom, Intel, Atheros, etc, not from the motherboard manufacturer).
If you've made any changes to the network config during the LAN (fixed IP, different DNS, etc.), make sure to undo them.
Windows caches stuff about machines and networks its been connected to, try flushing the ARP and DNS resolver caches.
Make sure there aren't any network-demanding applications running in the background (DC++, torrent client, update stuff).
Install Wireshark, check to see if some background service is flooding the network.
Scan for malware.
Boot from a Linux live cd (Ubuntu is fine). If your network issues disappear then know that it's unlikely to be a hardware problem, if so, just reinstall Windows.
Try installing a PCIe ethernet card and see how that goes.

GW2 · July 4, 2017

IP conflict maybe? did you have to set a static IP when you went to the LAN party? check that your IP settings are set to automatically obtain from DHCP server, check the DHCP table on the router and make a note of all IPs connected when the PC is off and then when on, see if you see any conflicts.