Boot device failed when trying to boot clover usb

I made a usb with unibeast, put the kexts I needed and plugged it into my pc(dell optiplex 990). I went to the boot menu, tried booting the usb and it says boot device failed. I’ve tried reinstalling, making the usb through terminal and using the clover program to get everything else and nothing has worked. I’ve tried mbr(a total mess went back to gpt). Help