I booted from the Xubuntu 18.04.1 Install ISO, installed qemu, copied and modified some files to adjust for user name and permissions, and ran my Windows 10 qemu-system-x86 script - same result (black screen displays and qemu-system-x86 runs at 100% cpu indefinitely). Totally black screen immediately - no bios flashes.
Therefore, it appears to me that the problem is not my Xubuntu software setup.
I booted from the Xubuntu 18.04.1 Install ISO, installed qemu, copied and modified some files to adjust for user name and permissions, and ran my Windows 10 qemu-system-x86 script - same result (black screen displays and qemu-system-x86 runs at 100% cpu indefinitely). Totally black screen immediately - no bios flashes.
Therefore, it appears to me that the problem is not my Xubuntu software setup.