My PC started lagging and stuttering about two weeks ago. It happens in video games and also while watching YouTube, where videos may become choppy, buffer, or freeze briefly. Every other device in the house works normally, including consoles, TVs, and phones, and my internet provider found no issue with the connection. The computer has an NVIDIA RTX 4070 Ti Super and an AMD Ryzen 7 9800X3D, so it should easily handle both gaming and video playback. I already reinstalled the NVIDIA graphics driver, but that did not help. I have not knowingly changed anything major, so I am not sure what to check next. What could cause this problem to affect only one PC, and which temperatures, CPU or GPU usage, background processes, Windows details, or network tests would be useful for diagnosing it?
2 Answers
It would also be worth running a malware scan. Download Malwarebytes from its official website, decline the optional extended protection trial if you do not want it, and run a one-time scan. Unwanted software can consume resources or interfere with browser and game performance, so this is a useful step when the problem began suddenly.
Open Task Manager with Ctrl+Shift+Esc while the stuttering is happening. Check the Processes and Performance tabs for anything using an unusually high amount of CPU, memory, disk, or GPU resources. A background process maxing out the system could affect both games and video playback, even if the graphics driver is installed correctly.

I checked Task Manager and took a screenshot while the issue was happening. I’m still not sure which numbers or processes are abnormal, so I may need help interpreting it.