pc randomly restarting

greetings so i bought new components few days ago and this started happening. my psu is the only thing that i did not upgrade because it is 700w and it lookeds like its working fine ... all the rest were upgraded and now when im playing games , at random intervals my pc restarts with NO errors...

Hello, I'm currently having problems with my ~12yo setup (only cpu, psu and Mb are this old) - it was always working perfectly without any problems but now for few days computer just restarts (Skipping any BSOD's/errors whatsoever) after 20 minutes of high end games (Witcher 3, Dark Souls3, ArmA...