@Jiryn It could be that those cards are not compatible with the pi3, or they could be bad. Stick them back in your pc and run a check disk on them. Here is a list of compatible sd cards https://elinux.org/RPi_SD_cards Your cards do not show up there but a 256 Samsung EVO PLUS is listed as compatible. If you want more space you will likely need to consider using a usb mounted hdd or thumb drive. Here is another relevant discussion https://retropie.org.uk/forum/topic/783/largest-size-micro-sd-card