watchdog error, sleep and lockscreen freezing, and stable under some load tells me either the cpu isn't getting enough voltage if it's manually oc'd, or there's some bios or os powersaving thing malfunctioning.
reset bios settings, especially if you've done any overclocking. turn off any core boost or other variable core clock powersaving amd/intel specific 'features'; these are almost always unstable in my experience.
if that doesn't work, double check all power cables are properly seated in both mobo/component side and psu side if it's modular. make sure ram is seated properly. if you're on windows make sure you're on high performance mode. i can't think of much else to check without more info. good luck!