Computer boots into Ubuntu just fine, but skips the bootloader screen
I'm really keen to give my Mac Pro (Mid 2012) a second life as a Plex server. The problem is, last time I was tinkering with it (2 years ago), I loaded Ubuntu on it and messed up the bootloader while trying to configure dual boot with rEFInd.
This would all be fine, but I additionally forgot the password to the Ubuntu user. This means that I am unable to repair the bootloader, which would allow me to load a new OS onto the computer, along with a known admin password.
I'm wondering if my GPU also has issue as only the MiniDisplay Ports work, and not the DVI, which could lead to issues displaying the bootloader screen upon startup.
I've tried NVRAM reset (chimes ones, black screen). I've tried holding Option when I boot (still black screen). I've reseated the RAM. It's just a strange problem. I figured I could just load a new OS on, but the only thing I get is the Ubuntu splash screen and then Ubuntu's desktop (I set it to automatically log into the user, but I have no sudo access).