ERROR -1073741819 (0xffffffffc0000005)

This could have to do with memory. You can install "WhoCrashed". This is a free download and shows often but not always, what the cause is from a blue screen or reboot.

That's your Win8 box that's doing this? I don't see that host ID. I see three boxes - the WinXP box hasn't been heard from since Dec 2012 - and the Win 7 box seems to be a champ. Where are you seeing the C thousand 5 error? None of your hosts show WU abends.

The 7-zip benchmark should be run for sevreal iterations with the largest dictionary size that it'll allocate. Let that run for about 30 minutes. That should be a pretty good test of the RAM. If it passes that, I'm unconvinced there's a problem with RAM modules.

Quite frankly, if it passes 7-zip benchmark, I'd run Prime95 for a few hours. That's going to stress test the CPU & the memory sub-system. If it passes 7-zip and fails Prime95, the prollem is either the CPU or the mobo.

Check the air intake on the CPU cooler. Make sure its not clogged with dust. Vacume that crap out while using a trim paint-brush to get into the fins of the heat-sink. A little bit of dust isn't going to be a prollem. Its the mondo-to-grimace proportion doorway-darkening wooly-boogers that are highly suspect as gremlins here. If it really was caked on, then removing the fan from the heat-sink may be what needs to be done here so as to get in between the heat-sink fins. Or shoot compressed air into it and spew dust all over; at least it won't be in your CPU cooler.

Speedfan is a decent free utility to implement for CPU / GFX / mobo temp monitoring and fan control. Your CPU should be at < 60 deg. C. at full load. But unless temps are in excess of 100, the CPU should just throttle down. Thermal trip don't happen with the newer CPU like in the peterodactyl days.

If the fan on the CPU cooler isn't spinning at all (or very slowly), SpeedFan will tell you that the CPU fan isn't spinning (or spinning very slowly). If the CPU fan isn't spinning (or spinning very slowly), it'll tell you that the CPU is pretty warm too. OR you could just watch the CPU fan and make sure its spinning; your call.

Its possible the PSU can be at issue. They can get wonky when they get older. How old is that one? 5 years is pretty much when you can begin to see flakey problems. Cheaper ones can go wonky in as short as two years. How many watts is it rated at? Ideally one wants to size PSU's at 200% of requirements. That's especially true for the el-cheapo units. This is more for lengevity than anything else. Heat kills electronic components, and the more stressed a PSU is the hotter it'll run (and by extension the shorter its lifespan).

SpeedFan has monitoring functionality for different power supply rails of your PSU. You shold be within 8% of nominal. If you observe spikes outside that range a metaphysicist would be a good consultant then. They're into the affect of electrical spikes and sags on how that affects feng shui and the chi of your PC.

Ideally you want to condition power to the PSU by implementing a batery backup unit that has smart-boost and smart-trim funcionality. The better units do that w/out tripping onto battery. One advantage to battery backups are that the better ones do power conditioning and filter out noise on A/C mains. Noise over time can play havoc with D/C circuitry of the mobo.

Albeit standby power supplies have surge protection, you want to have external surge protection. Ideally you want to discard surge protectors every 5 years. There's no way to discern how stressed a surge protector has been; death by a thousand cuts. Your secondary line of defense is the standy-power supply internal surge protection. Its cheaper to replace the external surge protection rather than the SPS. You want to spend $50+ on surge protector having the highest joule rating in quickest time. Once a surge protectors joule rating is exceeded its toast. If it sees 100 surges at 1% its max rating, the surge protector is toast.

There could be an issue with power quality on mains, i.e., either sags, spikes, noise, etc. PSU that's getting long in the tooth may not be able to handle transients as well as when younger. If you're using that 4 pole molex - for the CPU - power supply quality tolerances are much more tight than the older CPU's.

The other prollem child could be HDD issues. Bad spots on the HDD - either hard or soft - could cause C thousand 5 errors. Soft errors can be fixed with a HDD drive dx / repair utility. Hard errors intimate imminent HDD failure.

Spontaneous reboot suggests a mobo problem (if its not related to PSU). Check to ensure that system isn't configured to reboot on BSOD. That'll be in startup & recover settings. That way you can establish if the system is BSOD to reboot. Check the event logs too. There may be a clue in either the application or system event logs.