@strodown i use 18.07.13. anyway i already solved the problem. i use plop and it boots now.

i have hp dc7900 (core2duo E8400). i tried using portable x64 etcher but after successfully writing, boot files are missing. no start.elf, bootcode.bin,etc. only recalbox-boot.conf on the main. BOOT folder contain "grub" folder, bzImage, initrd.gz, EFI folder contain BOOT folder with bootx64.efi & grub.cfg. I cannot boot it even if I disable "data execution prevention" on the bios. No secure boot setting on my bios. I also tried disabling my main hard drive and only USB drive is set to boot. Should I use the old recalbox version, I saw a youtube video (a year old) that has different boot files than the latest recalbox? Need help please. Thanks