No display on startup normally means the TiVo BIOS couldn't find a drive to boot from, not that the drive is unbootable. Do you see the "welcome... powering up..." message?
Do the drives spin up? Have you checked the TiVo IDE cable?
You might also want to try maketivobootable as it sounds like your old drive was using partition 7 whereas your new one has been restored to partition 4. If the boot record points to 7 but the OS is on 4 then it won't boot.
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