grub install says it works, trying to boot from installation doesn't

I ran grub2-install successfully on /dev/sda1, so it reported, but when I boot, when I enter Code:set root=(hd0,msdos1)
chainloader +1
bootinto the grub> prompt, it returns me to the grub prompt. If an error is reported, it disappears too quickly for me to read it.

I used to boot off /dev/sda4 and installed grub on it, too. But I can't boot from any kernel installed on it anymore, not any kernel I built, not any package kernel, why I tried on /dev/sda1. If I set root=(hd0,msdos4), it boots but crashes.

I tried legacy_kernel, which returns Quote:

filename expected

even though I give it a valid filename.