My PSP is currently using Dark Alex's custom 2.71 firmware and I need to go back to 1.5. So I downloaded the Generic Downgrader, put it in the memory stick with the 1.5 firmware. This PSP is a Japan launch model so it works with every FW down to 1.0.
I followed that sticky guide on using the downgrader but when I start the program, it resets the PSP. The PSP logo screen appears, then turns the system off, and re-starts it like a hard reset. Since I can't find a troubleshooting section for this kind of problem, I decided to look for answers here.