The 0x000000 signature can be many causes, it’s simply not able to communicate with the chip. Did you successfully change any fuse bits? I doubt it but just want to confirm as a factory fresh chip should always flash okay at least the first time since it defaults to the internal clock. Once fuse bits are changed, an incorrect clock configuration can appear to brick a chip.
Go into the ide preferences and turn on verbose upload and try again, posting the result from the output window of ide using the </> icon (code tags). That will hopefully provide some clues.