Well, VSync didn't work. Now onwards to power saving mode. If it fails too, i will try all things suggested here, in order, one by one.

I HAVE a cooling pad which works perfectly. And pc shuts down entirely, no reboot.

UPDATE: Power saving mode seems to have solved the issue! Thanks for the suggestion! Something so simple, quick and easy to do and trivial to know, kept me captive all this time... I still am a pc noob, alas.