OK. You've provided very poor information. "Won't boot" could be ≥100 errors, but you don't narrow them down - at all.
From the screenshot, your kernel is loading, so grub is finding your kernel anyhow. But there's 3-5 screenfuls of that; We need to see the end of your text output. What happens then? Are you 32/64 bit? Gentoo what? Reboot a couple of times until you know where the end is and post a photo of that.
You can also press 'e' when you see grub. On the end of the boot line, stick
and if you know linux, you can try stuff from there. But if you're new to linux, you mightn't get far this way.