Mac booting loop, I can't recovery or boot from USB
You might want to try to boot into Verbose Mode. This is a regular boot process, however, the graphical screen is turned off in favour of a terminal-like screen logging everything that happens during boot. This may give you the chance to see an error message indicating the cause of your problem. It is not too likely yet still possible so do give it a try.

To boot verbose you need to press cmd-V upon startup. You may release the keys just after the boot chime has passed. The screen should immediately switch to a white font on a black background. You need a fast eye to read these (cryptic!) messages as you cannot hold them. 

Good luck!