Since your iMac even won't enter Safe Mode and macOS Recovery mode, the first thing I have to mention you to do is, to check your power cord and outlet. You can change a power socket to verify whether the damage of it or not makes your iMac fail to get enough power to support itself turning on.
If useless, try the following tricks to fix your Mac not booting up (only for Intel-based Mac models):
- Reset NVRAM. This is to refresh the corrupted OS-related settings that stop you from accessing your iMac.
- Reset SMC. SMC controls battery and power-related settings. Resetting it can exclude the errors in SMC that block your iMac from starting up.
If these ways change nothing, you'd better contact Apple support to find a better way to repair your new iMac.
