Dell E5420: Cannot boot into Installer

Hi All,

i am trying to install El Sierra on this laptop. I created an installation USB stick using Unibeast. However, the kernel seems to be unable to find the root file system (see attached photo).
How can i make the USB ports visible to the kernel?

Hardware:
CPU: Intel Core i3-2350M
Chipset: Intel HM65 Express
VGA: Intel HD Graphics 3000

I am using Clover legacy boot since UEFI support is not properly working with this model.

Thanks for any help! View attachment 226626