""If i take off vsync after 15-30 min playing i got black screen or coloured strips on my screen, sound is blocked and i must restart pc.""
Answer: Don't disable vsync while playing.
I think what kingfish means is that the problem when vsync is off is usually excessive heat and/ or unstable clocks and voltages that can/ could lead to driver or system crashes.
Vsync matches your fps to your monitor's current refresh rate. For example, if you use 1080p resolution and 60 Hz refresh rate for your monitor output, then enabling vsync while gaming will limit your in-game frames-per-second to 60. Disabling vsync will cause your game to render more frames, thus using more gpu power and that means more heat and gpu stress.
Now, if your gpu is not cooled properly or is overclocked/ overvolted, or both, then it can lead to ctd, bsod, lock-ups and so on. Or maybe it just shows instability when stressed.
Assuming your PSU (power supply) is up to the task and provides sufficient power to the gpu and the rest of the PC components when your system is stressed, of course.