Same problem. S1200BTL motherboard and trying to install ESXi 5.5. USB keyboard works for BOIS and to launch the install from CD but after the file copy and the ESXi Installer starts up, all USB keyboard function is lost. Tried all USB ports with different USB keyboards connected - one on front USB port and one on rear. Both keyboards would work in BOIS etc. but about midway through the Installer screen where it is split black/yellow, I noticed that the num lock light would go out on both keyboards and from then on nothing worked. Finally, I figured that a USB card with a different controller might work - I have an old PCI USB 2.0 card at home. I popped off the cover to verify it had the necessary PCI slot (I could have just looked at the Quick Start Guide sitting next to me but for some reason didn't think and popped it open). Then I saw the internal USB port in the corner by the SATA ports. Just for grins, I tried one more time. This time when the num lock light went out, I hit the num lock button again and the light came on and stayed on (coincidentally, the other kb was still connected to the rear - it's light went out at the same time but no matter what, it would not come back on - it was DOA like all the previous times. Using the internal USB, I successfully completed the ESXi 5.5 install.