Especially given the behavior of the power button, I would implicate the motherboard. As someone also using a P55 LE, and having recently gone through freezing/hanging problems of my own, I would bet that these freezes would be resolved by BIOS A74.
Does your system by any chance also include at least one WD VelociRaptor hard drive, or some other 10,000+ RPM drive? I suspect that BIOS A29-A59 suffer some misunderstandings with these drives, as I was noticing during my freezes that my two WD drives would suddenly sit at 100% active time while my two 7,200 RPM Seagate hard drives would remain normal.
Sadly, these problems are terrible to track down as it could be hardware or software. A game I run recently has "anti-cheat" sw installed (installs driver and 2 monitor processes). One of the things it does is hooks the keyboard interrupt. Unfortunately, it's buggy and doesn't always remove itself properly on game shutdown -- this causes an eventual lockup -- either on shutdown OR upon restarting the game.
The bit about terrible sound coming out -- does that only happen when sound is already coming out of the speaker? If it starts up on freeze, that's even weirder, but usually if sound is playing, and the process supplying the sound to the card doesn't provide new data to the sound-channel, whatever is in the sound-output buffer is often repeated ad nauseum causing a NON-random repeating sound of some sort.
Since you note that the keyboard light doesn't toggle, this points to a software problem -- as the only IRQ higher than the keyboard is the system time, which I ****think**** is used for scheduling. However, since drivers also deal with HW, it could still be HW giving some SW-driver bogus info, that causes it to lock up.
On the HW side, it could be a power spike (not real likely, but as someone mentioned, a power-conditioning UPS (one that emits a clean sine-wave) would be one 'test' (as well as a good addition in protecting against power spikes). A end guess would be temperature related (do you do any temperature
monitoring? Might try free util "Open Hardware Monitor" from http://openhardwaremonitor.org/. Only really does GPU+CPU, but should give you an idea of temps and whether or not hangs happen when temps are up or not.
But on SW side, besides making sure you have latest drivers for your HW, you might try disconnecting any HW periphs you don't need while you are playing a game where hanging occurs, as well as shutting down all possible background SW and services.
Has this thing hung from day-1? Too bad you can't easily try Win7 as Win10 has been implicated in lots of SW-compat probs. If hang has become more frequent over time, have you cleaned dust out of inside of PC? (cooler and anywhere a fan might blow -- be sure to ground yourself before taking off parts... and be sure to unplug and bleed off capacitors. I've killed more than one piece of HW due to either static or not ensuring there was no residual power. I assume there is no time of day, day-of-week (or days of month) that hanging happens more often? Can I also assume that it doesn't matter what game you run?
The fact that it happens more on some games than others -- and from your description, seems to be more demanding games, makes me think graphics card power+temp. Are you able to try a newer graphics card? Specifically a GTX1070 or GTX1080. Don't laugh just yet....reason I asked... I had a GTX980 and had more flakey probs related to graphics.
Side note: I had to buy a new power supply because the 1100W
included by Dell didn't have the right hookups to support two full
8-pin connectors for extra power (It was a design flaw in their T7500
-- that you could even see in their maintenance manual photos. Two of the 12V 75W pins available for extra graphics card power were on the
same RAIL!). I had to replace it on my dime w/a 1300W -- and that
eliminated a bunch of probs. However, the card was a dual-GPU card
that ran hot -- and that added it's own flakeyness.
ANYWAY -- Nvidia's newer cards -- like the 1080 -- take less power! -- only
2 6-pin connectors -- and it runs cooler! So...if your current card is running toward the hot side, I found the 10XX series to be pin-compatible w/the older models (will auto adapt to older PCEe standards at some perf-loss).
When I had the Dell power supply in my unit -- usually things would run fine -- and usually did, except under certain types of graphical load. Like when I did the Win7 hardware-rating test -- one of those tests caused the machine to reliably reset with a 980 card.
The fact that you are noticing a pattern is GREAT -- gives some hope of figuring this out. Hope I gave you some ideas, -- since these issues are often notoriously hard to pin down. Good luck!
Best Answer
Given the description of the freeze you're describing, it does sounds like a hardware-level issue, however not necessarily caused by the CPU. That said, a multi-CPU system can definitely tangle itself into a deadlock on all cores, if each is running a thread or process that are each waiting on a resource the other thread/process has allocated. A search on "CPU deadlock" provides lots of details on possible conditions. A failure due to overheating or improper voltage settings could also cause intermittent behavior - although I've only seen systems shutdown or refuse to POST when this is the case.
FYI - I've seen similar problems on systems with bad memory sticks, and bad video cards. You might try running some burn-in diagnostics such as MemTest+, and/or benchmarking the system with different pieces of hardware removed to see if you can isolate the unstable component(s).