Need some directions to determine what to check on my Computer

Question

My PC has been lagging badly lately. At first I thought I may have installed bad software or may have been a virus but it wasn't the case. Ultimately I've chosen to reformat my Windows 10 PC and so far I've noticed that I still feel the lag happening.

The lag that happens to me works like this: I browse some sites, my browser (firefox) ends up not responding. Sometimes I browse through my files and it also ends with my pc not responding for a couple of seconds before resuming what it was doing as if nothing happened. It also happened with games. I played Fallout 4 and there would be times that my pc freezes for a couple of seconds similar to when I browse the net or just go through my files.

I've ruled out software since I already reformatted so I'm thinking it may be hardware. I doubt it's my GPU since I bought it fairly recently and it wouldn't affect explorer or my browser right? I did a memory diagnostic test and nothing shows up. SMART tests show all my HDDs are fine.

The only possible hardware I haven't tested for possible failure would be the PSU processor and mobo.

I haven't heard beeps from my Mobo so I think I'm safe there but are there any other ways to tell if its going bad? I don't know how to check if processors are going bad too since it never happened to me before.

I originally thought my hard disk was the component at fault because there was a time that my pc would suddenly restart and couldn't detect the said hdd (doesn't show up on bios at all) so I replaced the sata cord but it still happened and at that point i chose to replace it with a WDC Blue and the sudden disappearing hard disk thing didn't happen anymore but the lags were still there. I replaced the sata cords and swapped the cords powering the drive as well and it didnt change anything.

Specs:

• 8GB DDR3 Ripjaws
• AMD Kaveri 6400 (Installed a Gammax400 hsfinstead of using its default hsf)
• Radeon 270X
• Antec HCG 620-M
• Gigabyte F2A88XM-HD3
• WD Blue (Where my OS is, and it was newly bought)

Is it possible that my processor is really just crappy? I mean I know its not the best out there but my pc hasn't been lagging like this a few weeks ago.