Legacy PC, OC not booting

Hi guys. I just want to say that I've just figured out that, v3 High Sierra dmg file had clover installation, not OpenCore. (In my other post, i thought it was also OpenCore) And now I'm trying OpenCore's guide but can't boot it. After i picked the usb, get a long dark screen, waiting, then i get a gray screen which looks like a BIOS, only says continue, boot manager and 2 things more, not OpenCore screen. Can't see OpenCore no matter what i try. Any suggestions? Thanks!

Author: @dogukan55209