Fixing HDD and CPU always up to 100%

Today I could fix a case where a computer got incredible slow over the years, but it took to check lots of points...

First of all the issue was initially hard to figure out where it's coming from. 

Either the HDD in the Task Manager went up to 100% or the CPU - or both together. Even when no application was started. Narrowing down which service or application was at fault was difficult as well as it was always another one.

So I tried first with the 'obvious' solution which you find quite often online: Switching off services like 'Windows Search' or 'Superfetch'. Initially it seemed like no change at all. I even checked the hard disk since I even found sites where users where claiming having issues with the Toshiba DT01ACA100. But the HDD was fine so far, nothing visible with checking tools.

So what else... Such issues can come through viruses or malware so I gave Malwarebytes AntiMalware another go. And it found more than 4000 suspicious entries! After clearing them all and going for another reboot, let the software went through after to check if the malware is really gone and suddenly the issues got less!

Surely, right after booting the computer still took a while 'calm down' in terms after processor and hard disk usage. But then you could finally reproduce it by opening the Firefox browser and open certain websites. Or starting MS Office software.

Generally websites using flash took pushed the scale high again, but after certain tests to fix that issue within FF failed and I tried the same with Google Chrome which was faster and and slightly better.

And now after several restarts the computer finally seems fine again - hopefully it remains!

A slowly dying ASUS M5A99X mainboard

Initially the cause wasn't clear. The computer was in some situations very slow and caused problems while agreeing admin permissions to install applications...

First I was informed to take a check from remote, but that wasn't even possible. The other site of the line had problems installing TeamViewer, the computer hanged at the moment UAC popped up for agreeing admin permissions. At the moment nothing happened anymore. After the next restart the computer itself got even slower. A few spots on the taskbar didn't even work anymore.

Seeing the difficult child myself, I just checked the basic stuff: Hard disk is fine, booting an alternate OS by DVD worked without issues, no malware or anything like that. But the issue got worse, at every attempt even slower!

After another test I wasn't able to start the computer anymore. The screen turned on for a moment but that was it. It remained black. Removing all drives didn't make any difference.

Ok.. so what's going on? From now it was clear it's a hardware problem. I did a BIOS reset (RTC RAM), restarted and the boot screen appeared, but unfortunately the screen froze from that moment on. I could press any key for entering Setup or changing the boot order - nothing happen. I turned off and there was the black screen again.

A few other ideas:

• Removing all boot devices (HDD, DVD)
  Booting without any RAM
• Booting without graphics adapter

While doing this tests there wasn't any beeping or difference at all. The motherboard must be damaged! Else there would be any beeping alarm or a kind of warning that something's not attached.

To be sure, I ordered a new Asus M5A99X board in order to make sure it's really the issue. And I was right: I changed the board, moved the CPU, the cooler and everything else to the new motherboard and the computer started again. 

But that's not the end of the story: After a successful restart the problems didn't really vanish. The Windows system was obviously damaged, too. I knew that the hard disk was ok, so I created an image of drive C and reinstalled Windows 10, basic software and updates. Now it's all working as fine as it should be. I copied all necessary files from the image back to the user folders and that was it...

Damn motherboard, whatever happened there...