what is the problem:
My raspberry pi 3a+ won't connect with the internet so I can't run octopi.
What did you already try to solve it:
I have tried an other raspberry pi 3a+ and a new micro sd card.
It had worked 2 times but the green light from the raspberry pi won't light up anymore. If I put the micro sd card in the laptop, the laptop gives an sd card error.
Unfortunately, I don't have any suggestions for the "won't connect with the internet" problem but I can comment on the "micro SD card in the laptop" problem.
When you use an imager to write the micro SD card, there are two partitions created. One is FAT32 and contains the /boot files. The other is a Linux EXT4 partition that contains the root (/) filesystem. When you insert the card in the laptop (which I assume is running Windows). The FAT32 partition is mounted but Windows can't (without some help) recognize the EXT4 partition so it complains. Just ignore the complaint as there's nothing "wrong" and don't "format" the card as Windows might suggest.
Thank you. Can I format the micro sd card with windows if I want to empty it for the imager or should I leave that to the imager itself?
You don't need to format it before imaging, the imager will do that as part of its process anyway.
ok nice. I'm running Octiprint now. I have put the wifi network in the boot file myself. Now the raspberry pi 3a+ does connect.