Since it seems to be when you browse, did you reset the browsers? It happened to me and what a pain to diagnose.
Couple of days ago My Pc experienced a sudden slowdown. I tried troubleshooting to no avail. The next day i took it to a PC repair shop and they replaced and copied the previous hard drive. When i got it back today it was still extremely slow. I ran full system scans with Spybot and Malwarebytes which both turned up nothing. I didn't do anything out of the ordinary when the coputer slowed down. Just watching a few streams then i started noticing lag.
Symptoms are as follows: When turned it on it works fine for a few minutes then slows down tremendously.
The CPU usage goes haywire. I checked all the processes in task manager and there isn't anything out of the ordinary. I don't know if there are any hidden processes.
When i move my mouse around the cpu usage jumps about 20%.
It takes about 4-6 seconds for it to respond when i try to open a webpage.
The cpu usage sometimes jumps to 99-100%
Mean CPU usage stays around 25-35% when idle.
I left the PC on overnight after this happened and when i went back on in the morning it was fine.. then slowed down again after a few minutes
I was almost positive it was a problem with the hard drive but since I now have a new one it doesn't seem so. Please help!!