Once you enter Factory Service Mode in any FW above 3.55 you are stuck there. No one has figured out a way to get out of it, not since i last heard neways... Time for you to invest in a new PSthree... 4.21/4.25/4.30 CFW is Great by the way ! See you when you get there !
Can't you just re-flash the 3.55 dump? In that case you would need a hardware flasher such as Progskeet or E3. Haven't tested this, but a flasher is cheaper then a new PS3, so It might be worth It. I'll search and see if anyone has tried this.