Crash/restart mystery something to do with the case or PSU?

[ouch]

My wife has a PC I built a 3 years ago:

MSI h97m-g43
i3 4160
No video card
Corsair CSM450W PSU
FD Define Mini case

She uses it for work, and it's often left running for days on end, with hardly an issue. Recently it's started behaving a bit odd.
It appears to get stuck in some sort of restart loop - power light will come on, fans will start, then it's click and shutdown, wait a moment and the repeat.
If I take the side off the case, it'll start up and run peachy - this is not optimal as we have kids, and I don't want to find lego in there.
Occasionally (twice so far) she'll be working and then it'll crash, not BSOD or anything, garbled screen output and complete freeze.

All fans spin, and I've installed coretemp, but it's in a cool room, and this time of year it shouldn't be suffering (she doesn't work it hard).
Now I'm wondering if it may be a PSU issue? Startup inrush or something? but before I go buying/swapping parts, has anyone else had this problem or similar?

Update: Swapped PSU as I needed to look like I was doing something (Had an identical one in my system). Ran fine for a bit then went and reset itself - apparently it gave a warning before shutting down but it was so quick didn't get the change to read it. I've since used the bios to up the fans to max, coretemp is reporting 23-24 deg CPU which is pretty chilly IMO. Mine is still running as normal, so I think we can rule out the PSU.

Would a BIOS check/update be worth doing?

 

[GhislainG]

If the system works fine with the side panel off, then something overheats (probably on the motherboard if the CPU is cool) when it's on. A BIOS update can't solve that issue; you need to check if the motherboard and filters (if any) are clean, if the fans spin fast enough to keep a good airflow, et.

 

[ouch]

I make a point of cleaning out the filters and whatnot every couple of months, and whilst I wouldn't recommend you eat your dinner off it, the motherboard and heatsinks are fairly clean and dust free.

Since the BIOS fan speed tweak (all running at max), I've yet to see a crash, I'm trying to test further by stress testing the system. The problem is I'm not sure if it'll be the board or the processor - I have a spare processor to swap in, but replacing the board will be a bigger headache.

It needs to be reliable as my wife uses it for work.

 

[GhislainG]

It's easy to test the CPU; run Prime 95 Small FFTs for several minutes and the worst that should happen is throttling if you use the stock cooler.

 

[ouch]

Ran some 15 minute stress tests using some burn-in software, temps peaked at 59deg which is fine by my books. I might put the fans back on a dynamic profile and try again - this will tell me if the fans aren't up to snuff.

 

[GhislainG]

The application you used either isn't very stressful or you have an awfully great cooler. My 13-4170 runs a lot hotter than that while stress testing it with Prime95 Small FFTs.

 

[ouch]

It's the stock cooler, so I suspect it's the app not working it too hard. Will try Prime95 when the PC is free.