Flashing folder at start up, all recommended troubleshooting has failed
Hate to say it, buddy, but if disk0 and base system are all you got, and if base system is part of disk0, your MacBook Pro isn't seeing your hard drive. Reset the SMC if you can (Shift+Control+Option+Power while plugged in, then press power again after releasing all keys.) But if that doesn't work, it's either the SATA controller, the connection to the drive, or the drive. At that point, it's a store visit.