I turned on my computer this morning and it turned on normally, then it turned itself off on it's own 5 seconds later. It then decides to automatically try to turn on again and gets stuck in an infinite loop of starting up and shutting down every 5 seconds. I checked inside and found error code 55 on my motherboard a Z77 Extreme4. Apparently this is a memory not installed issue,but I haven't touched my memory sticks since I built my PC years ago and have never had memory problems.

I'm currently posting on a different PC. The thing is I want to be sure what the problem is before I buy anything and my computer won't let me access the UEFI menu or even get a video signal for a memory diagnostic. I need a way of finding out what the problem is and I don't have any spare memory sticks lying around, though I could pull them off an ancient PC, but that might bring compatibility issues. What's the best way to troubleshoot this one? I'm also not 100% sure about the code since the PC I'm on right now has compatibility issues and some pages won't load.

try removing and reinserting your ram maybe?
only need 1 stick to get a post not all.

Taking them in and out didn't work, but switching the slots did. Memory diagonstic didn't say anything was wrong. Is this a deathflag for my RAM or does this just happen randomly for no reason at all?

you may have not inserted them fully.
but if they still don't work in "X" slot then the dimm slot itself may be bad now.