Have a look here:
https://3ds.guide/troubleshooting. If it doesn't help you can tell the symptoms here and we might be able to help.
Unfortunately i can't try any of those things because i can't access gm9, I'll type out what happened.
Randomly 2 of my buttons stopped working properly, the Y and sometimes B button. I'm not sure how this happened because I only noticed this after an extended period of not using my 3ds.
I open my 3ds in an attempt to clean off the buttons with some compressed air (I open it up a put it back together twice because the first time I didn't get the results i wanted, which was a working Y button)
When i put it back together and try to turn on my 3DS it doesn't work at all.
I'll power up the console and it will stay on for about 7 seconds, I'll a POP sound and it turns back off. ( I'll also mention that when i plug in the charger the orange light will stay on for about the same amount of time.)
Pressing either Start or Select turns it off immediately as opposed to waiting 7 seconds.
I tried moving the essential boot files (boot.firm and the luma folder) to another micro SD and i get the exact same results
Someone else i was speaking to suggested that the SD reader for my console might be broken.
I'm 80% sure that I didn't setup CTRNAND Luma3DS or whatever that thing is called that allows you to turn on the console without having an SD your SD card inside.