Mid-Range Computer Running Slow after being off for a month

[TheSundanceKid]

Recently I came back home from a month-long vacation and when I got on my computer, it was a whole lot slower. At that point I was running windows 8. I ran a scan with Malwarebytes and deleted all the unwanted programs, and even one malicious program/folder. Afterwards I upgraded to windows 10 and it's still just as slow. Before all the vacation it was pretty quick, and I could run most video games at max settings with a decent FPS, now it will barely run the games. It can't be the ping because whenever I did play, it was always pretty low. And I don't think it could be malware or anything because I ran another scan today and it came up clean. I should also say that last night my computer shut down because the CPU was getting too hot, so that might be the cause, even though it's more-or-less dust-free in the tower. Simply put, I have no clue why my PC is slow as all hell, and I just need some advice as to why it is and how to fix it.

Some specs of my PC, just incase it's important.
CPU: Intel i5 4670K 3.4GHz (watercooled)
GPU: Asus GTX760
just ask if anything more is needed.

Update: Pump is not working.

 

[getochkn]

Is your CPU fan spinning. If it's too hot, it will first start to throttle itself down speed wise, and that will make it slow. As it continues to heat, it will eventually shut itself off, as you said it did.

 

[TheSundanceKid]

Is your CPU fan spinning. If it's too hot, it will first start to throttle itself down speed wise, and that will make it slow. As it continues to heat, it will eventually shut itself off, as you said it did.

Yes, both fans for the CPU are spinning, forgot to mention the fact it's water-cooled.

 

[getochkn]

Pump working? what are your cpu temps. If it says it's overheating, the first thing to kind of do is to monitor your temps.

 

[TheSundanceKid]

Pump working? what are your cpu temps. If it says it's overheating, the first thing to kind of do is to monitor your temps.

Well the temps on all the cores are currently around 100°C, so I'm gonna assume that the pump is not working because I don't remember hearing it turn on during start-up.

Update: Pump is in fact not working.

 

[getochkn]

There you go. Is it a custom water cooling loop or closed cooler?

 

[TheSundanceKid]

There you go. Is it a custom water cooling loop or closed cooler?

It's a closed loop. It's a corsair, but I forgot the specific model. I'm thinking like an H80i or similar model.

 

[getochkn]

check the plug, make sure it's plugged in or try switching the power source for it.

 

[TheSundanceKid]

check the plug, make sure it's plugged in or try switching the power source for it.

I wiggled the plug and made sure it was fitting and snug, turned it back on and still doesn't work. I can't find another place on my motherboard to power it either.