Lately I had been testing a lot Windows 8.1 and WinPE generated from Windows 8.x (i.e WinPE 4.0, 5.0, 5.1).
The Windows QEMU I had (lots of versions out there) was giving me a windows error 0x0000005d which means UNSUPPORTED_PROCESSOR .
Indeed, starting with Windows 8, you need a processor that supports NX/PAE/SSE2.
NX is not supported with older windows QEMU versions.
More details from MS here.
Googling around it appeared the solution was to use the -cpu command line parameter with QEMU.
Unfortunately, none of the QEMU versions I had was supported that parameter.
I then found the right (and latest) windows QEMU version (2.0.0) here.
I downloaded this version qemu-w32-setup-20140418.exe.
The command line :
start qemu-system-i386.exe -L .-m 512-cdrom D:\WinPE5.1.iso-cpu Nehalem allowed me to boot my latest Windows 8.1 with success ! 🙂
Also, note the use of coreinfo (from sysinternals) to check your processor flags.