18.04 freezes/purple screens after grub; nomodeset doesn’t work

I just installed ubuntu 18.04 LTS onto a partition (dual boot with Win10) and it initially worked very well. On my next restart though, I was met with a purple screen (after the grub screen) that wouldn’t go away even with “nomodeset” added on in grub. My CPU is a 3200G with Vega 11 graphics if that matters.

I also have tried older kernels from grub but they all freeze after “loading ramdisk”.

Thanks!