http://imgur.com/a/QrHgq

The image shows a screenshot of my task manager that shows my cpu is only using 46% maximum while I'm running Overwatch, Vegas pro 12 while rendering, media player, skype, chrome ... (just to stress test to see if it could go above)

Monday it all worked fine, tuesday it broke, my renders now take 2h to finish ... :'(

And with fine I mean, it used to go all the way 99% cpu usage

 

This one shows the Hardware monitor

http://imgur.com/a/RVPT3

that says the load is 100% but task manager says only 46%, and my render is going half as slow as it used to

 

Can someone explain and how to fix this?

Looks like its running hot.   Try blowing away all the dust from the inside of the computer.

https://ark.intel.com/en/products/72164/Intel-Core-i5-3230M-Processor-3M-Cache-up-to-3_20-GHz-rPGA
your notebook really go throttle your performance, because +105C is max for the chip, if you're geo corerct 21 C outside shouldn't be the issue along with 28 today... or maybe it just need some rest?

So your core clock multiplier is about 12 right now?(26 or 32 max)

It's like clock mp = hours uptime=12 xD

 

70k handlers isn't good either 

reboot?

 

some serious crap about it 
http://forum.notebookreview.com/threads/i7-3630qm-throttles-to-1200-mhz-at-less-then-70%C2%B0c-if-turbo-boost-is-enabled.797300/

Allright, I cleaned the vent inside and also redid the thermal compound to be sure.

Everything works again now :D

CPU usage back to 100% (the problem was probably more that the speed was only going till 1,2 GHz and now it's back to 2,6 GHz as it should)

 

Thanks for the feedback ^^