Seems I am having the same issues as everyone else on here.
ESXi 5.5 ISO install via USB on fresh HD into physical box.
I recently had ESXi 5.0 (test) installed and had my keyboard and mouse working without an issue.
I ended up buying a license and started the install of 5.5 on a fresh system. No issues at first. Went into bios changed the appropriate settings, keyboards working (have used 5 completely different keyboards so far), was able to force a USB boot without issue. Finally after everything loaded up, I came to the black and yellow install screen. Like others stated before me, all keyboard lights died roughly 25% in. After the lights died, there was no response what-so-ever. Meaning, I am unable to install or quit.
I'm not sure about everyone else, but having input into an operating system is a pretty big thing for me. Especially during the install.
I am going to try and internal-usb this one, but I really do hope someone finds an answer to this issue. The more I search about it, the more I find, and no one seems to have a complete answer.