it mostly happens when after a while of being on. sometimes when i start downloading something, other times right after startup or in login screen. i have an msi g43 mobo, gpu is sapphire 7950HD, i5 4670k.
"my powersupply is brand new, 600w(enough for what i have)" the fact that its new and 600w doesn't mean anything. For example a new 600w Raidmax(maker od very low quality cheap units) PSU is still a horrible power supply(even though its 600w and new), they can't delivery their rated wattage and they deliver dirty power than can(and usually will) cause system instability and can even damage other components.