"An error has occured" seconds after turning on

Hello! I have a problem with my Nintendo New 3DS. When I power it on, for a few seconds everything seems okay and then crash to the black screen with information:

“An error has occured. Hold down the POWER Button to turn off the power, then turn on and try again. (…)”

The weird thing is also that sometimes it works fine for like 3 days and then this shows up for months making the console unplayable. Also I’ve noticed that even though wi-fi works fine and it should connect, it says “disabled”.

Please give me a hint what might be wrong. I have this console for like 5 years and played on it for a few weeks at best!