Unable to Boot from internal Samsung SSD, external usb works fine

White flashing folder after crash, been using mac in its current state for a year, SSD works fine in usb enclosure, tried reinstalling os still wont boot. drive appears in disk utility when used as an internal drive, but cannot be selected with startup disk.

EDIT: was able to boot from the SSD when it was inside, only worked for about an hour, and everything was extremely slow, closing safari would get a loading wheel, then and it froze again and i got the white folder after a reboot.