Question PC Performance Issues/Lag spikes

Apr 11, 2022
My PC has been running fine up until about 3 weeks ago. I had this PC built for me in 2016, below are the specs:

CAS: NZXT H440 Designed by Razer Mid-Tower Gaming Case w/ USB 3.0, Side-Panel Window (Black Color)
CPU: Intel:registered: Core:tm: i7-6700K 4.00GHZ 8MB Intel Smart Cache LGA1151 (Skylake) [+74]
FAN: Asetek 550LC 120mm Liquid Cooling CPU Cooler - Extreme Cooling Performance (Single Standard 120MM Fan)
HDD: 1TB SATA-III 6.0Gb/s 32MB Cache 7200RPM HDD (256GB Sandisk SSD + Single Drive)
MEMORY: 8GB (4GBx2) DDR4/2400MHz Dual Channel Memory (Corsair Vengeance)
MOTHERBOARD: GIGABYTE G1.Sniper Z170 SLI ATX w/ USB 3.1, 3 PCIe x16, 2 PCIe x1, 3 SATA Express, 6 SATA3, 1 Ultra M.2
VIDEO: NVIDIA GeForce GTX 960 4GB GDDR5 PCIe 3.0 x16 (Maxwell) (Single Card)

I'm having trouble determining whether it's an internet or PC issue...I am thinking PC because other devices have been working relatively smoothly (streaming services, Ps5, iPad, etc.).

I mostly play a game called "Old School Runescape" that plays on its own client. When using the client alone, I am experiencing lag at times, little lag spikes every 10-15 seconds I'd say. When I attempt to use other applications like Discord or Spotify along with the game client, the lag gets way worse (performance issues more than lag I guess?). This was NEVER an issue a few weeks ago. Nothing has changed in the last few weeks other than me cleaning my PC fans

I've used basic tools like Speedtest to see if its internet, but it doesn't seem to be. Anything else you guys would recommend to check that may help me narrow down the issue? I am not opposed to upgrading my PC, but feel like its not necessary if it was working fine up until just recently.

Apologies if I posted this in the wrong section. Wasn't sure where would be most appropriate (new here)