sudden idea why?

I have been using my desktop since last December, everything set up and worked fine.
I do use a WiFi for internet and haven't moved the router or my desktop ever since December.

last Saturday morning, I woke up turned on my desktop and noticed high pings in league of legends and low connections on discord and also slow speed on browsers.
Not only that but my headphone mic was extremely low and started hearing humming noise.
So I am trying to figure out why this has happened all of sudden.
I have googled some stuff and only possible reasons that I can come up with is electronic devices or cable wires interference?
Here are few things to be noticed:

1. This has started happening since last Saturday (July 6th), Have been using same router and desktop since December.
2.. Haven't moved router or desktop position since December.
3. My brother's desktop(in the other room) or cell phones are working fine.
4. I did started using my A/C in my room but its using a different cable from the opposite side of the wall and for couple of days every devices was working fine....
up until now.
5. Headset still has humming noise but its volume of humming varies.
6. WiFi speed has gotten worse.
7. Possible hardware issues? but Mouse, keyboard, graphic card is all functioning well without any glitches or other problems..

Here are things I have tried:

1. Unplug everything and plug it back in (did nothing)
2. Use the power cable for only desktop and nothing else (phone chargers etc...) did nothing.
3. Turn off the A/C (did nothing)
4. Power cables are touching the ground (not tangled up in the air)

so... I need help..or start to look for possible things to try to resolve this.
* I am NOT tech wiz

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That's the long and short story for WiFi

You won't change a thing and blammo, performance drops. It can be anything from a failing router, wifi card to a new neighbor on your same WiFi channel.

I don't see detail here such as distance, channel, if you tried other WiFi channels or can use 5GHz. For me 5GHz helps as the overlap issue isn't nearly as bad.

The other thing I run into is sometimes you find someone in the house running TORRENT, either on purpose or a malware installation (doesn't matter as both kill network performance.)

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As for WiFi..

as for WiFi, I do not use torrents nor my family does. It has worked fine this July but starting last Saturday started this sudden disconnects and random ping spikes in-games (have tried changing channels between 1,6,11 and still random spikes and unstable connections). But other cell phones and desktop in other rooms. seems not be effected at all. It could be my WiFi card failing..or damaged but
this does not explain why my headset started humming and mic volume being extremely low. Everything such as monitor, graphic card, keyboard, mouse is functioning fine. Just WiFi and headset mic seems like its getting interfered by something..I just don't know how to confirm this...or where to start.

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When I'm on a call to this.

We carry in another router, our laptop and USB WiFi sticks. Folk without spares are very stuck about where to start but since WiFi does do this we know to carry in the spares and start with a site survey.

You seem to be on the old 2.4GHz only setup. You left out answers to all my questions but here's the rundown of our process.

1. Pull out the phone and run WiFiAnalyzer (the free app on the Google Play Store) to see how many hotspots are in the area. Sometimes you can't work around the limits of the 2.4GHz system so you do that to warn them they may need to get to the new 2.4 and 5GHz router and why.
2. If that's clear then look at the distance issues.
3. Now out comes the USB dongle or router depending on what they have. Try one the other then both.

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