computer crashes

[Mate]

Hey so I already got several computer crashes where the sound will just lag and a low resoltuion windows 8.1 screen appears saying that its gathering information and the PC needs t o be restarted, this problem also occured several times on stock clocks too, so its definitely not the overclock, i also had PRime95 running stable for several hours. also  this always occurs while gaming, already had it in several different games. I also found it in the event manager thingy I think, since the time fits, because it just happened. Afterwards the PC itself wouldnt restart and say there was a boot error, I jumped into the BIOS changed my ratio from 42 to 41, because the BIOS message reported that it could be due to the oc, what still doesnt make sense to me, but whatever. I also had a look in that folder there, but there was no memory.dmp file (also searched through the complete folder).

PS: on a hot day the highest temp. I would see under Prime95 would be 75°C on 4,2Ghz

important specs:

i5 4690k 4,2Ghz 1,075V before, now 4,1Ghz 1,075V, but as I said, it also happened on stock speed 3,9Ghz

CM Hyper TX3

Silverstone ST75F-GS 750W 80+Gold, had a Corsair CX600 before, but died after a month or so