What cfw are you using? If your using kmeaw you can you this spoofer disabler that should put you back to 3.55 if it doesnt work then is the cert files that you changed. To put the cert files back onto your ps3 you need to (in a FTP server) copy the two cert.27.bak and cert.24.back files onto your desktop and rename them back to cert.27 and cert.24 and then transfer them back to your ps3 and overwrite the existing cert.27 and cert.24 files. Then try to use the spoofer disabler and you should be good.
spoofer disabler for kmeaw:
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