EDIT: Problem Solved! Thanks iCraveTacos and fowler002! Solution: toggle to flash0 in recovery mode to restore 3.40E and use Hellcats flasher to flash directly to 5.50gen-d3.

Quick version:
PSP Phat 1001
Was on firmware 3.40OE-A
Tried to downgrade to 1.5
Now I can only boot into recovery mode.

Details:
Haven't touched my PSP or stayed up to date with the scene in a long time. Going to be dealing with some surgery soon so I dusted off the old PSP. Wanted to update to a newer custom firmware but all the guides are for starting with an official firmware. So I found a guide to downgrade back to 1.5.

I followed it exactly, checked the hashes, so I don't know if that guide was bullshit or I fucked up somewhere else. Now turning on my PSP, it just stays black a while and then turns off. However, I can boot into recovery mode still.

I figure there is some hope because I have recovery mode, but I don't know where to go from here. Any help is very, very appreciated. Gonna be in the hospital for a while and would appreciate a nice CFW PSP...