RAM problems

[Jiggens]

First post here so if it's in the wrong place feel free to move it or whatever, but basically it's a problem that has already solved itself so no longer needs troubleshooting- but I'd just really like some insight into what actually happened, why it stopped working and how it fixed itself.

 

I went on holidays over xmas/ny and had my PC turned off for 3 weeks, when I come and hit the button to power on all the fans spin up like normal, but there's a solid red DRAM_LED and 'no signal detected' on the monitor. Tried 2-3 more times with the same problem. Removed the GFX card (so that I could access the MemOK button... i have a very tight ITX build), reseated the RAM, and powered on again, same problem, tried MemOK which didn't work at first but after a couple of attempts it succeeded and got a boot (into the good old 480p driverless onboard gfx barely usable because 1 icon takes up half the screeen). So figuring whatever the issue was it's fixed now, I reinstalled the GFX card, plugged everything back in aaaand no boot, same issue solid red DRAM LED. Went through the same process removing gfx card again and couldn't get it to boot again after many attempts trying a lot of different things (4 different RAM sticks one at a time in each of the 2 slots on the board, hard CMOS reset by removing the battery, booting with only monitor and KB plugged in, etc)

Gave up and bought a new computer the next day.

Day after that (today) I decide to try one more time, and the computer boots up first go with the gfx card and both original ram sticks installed

Back to completely normal working as it always has, so I guess I have 2 computers now, too late to cancel the order on the new one. Not even mad (well a little bit mad.. in my rush of freaking out about having no computer I bought my first store-built computer of my life after having home built every single computer I have owned since ~1995, because I just wanted to get up and running again and couldn't be bothered with a build right now)

 

So yeah, like I said at the start, everything seems fine again now but I would really just like to know if anybody has a clue what might have happened to cause the problem, and how it just "magically" started working again after my last attempt at fixing was unsuccessful, then it sat for a day untouched, and next time I tried it just worked straight up as though nothing happened.

 

I should mention too, this PC was built in Jan 2015 so it's 5 years old and has always been perfectly stable until this, only upgrade it's had is a new GFX card Jan 2019 and continued being perfectly stable for a year after that, up until this happened.

 

Specs

Z97I-Plus

i5-4690K

Corsair Vengeance 2x4gb 1600

GTX1060 6GB