What could be mistaken as a switch on the left side of the lamphead is actually the knob that tightens the lamp socket and holds the bulb firmly in place. Fully tightened, the little handle on the knob is more or less vertical and if you turn it counter-clockwise to open the socket, it turns about 90 degrees to the left, maybe even less (hence the potential to be mistaken as a switch). So if that knob wasn't completely vertical, it means that the socket wasn't fully closed and therefore couldn't properly establish contact.
Btw, the focusing knob is on the back of the fixture and as the socket's tightening knob obviously moves with the globe, it indicates the focal point position for each sort of globe (2,5K/4K) respectively.
Merry christmas,
Frank