To explain all the events, here it is:
-at first it froze randomly, even if i opened a folder or anything, and the video driver stopped working (Nvidia graphics card)
-managed to make the video driver glitch stop by modifying a certain registry (could do some research on that if needed)
-did a bunch of things with the help of rshaffer61, in the topic above (reinstalled many drivers, changed my windows theme to normal, not the aero one) - this stopped another 70% of crashes
-set my PC on performance power settings
-used DPC Latency Check to monitor my crashes, which now only occured upon opening any big-size video file (eg. HD clips), and disabled "VIA 1394 OHCI compliant host controller", which made the crashed disappear, with the exception of internet videos (eg. Youtube)
I tried disabling about everything which could be safely disabled from Device manager (there are some system devices which i haven't touched, and could be a possibility, but not sure what they are for). Tried disabling every network adapter or sound device (even the ones from system devices).
The problem now is only related to video streaming on the internet, at the very start of a video i get a slight delay (2 red spies on DPC Latency check), and every now or then it freezes my pc, needing a restart to fix.
I've searched a lot to solve this problem, I could see that many people have a variation of it, but I have tried many things and I'm running out of solutions.