There is a difference between not turning on and no power at all. Do you have a standby light on the front when the unit is plugged in? If not, then I would first verify that the fuse is OK. If it is blown, try another. I suspect though, if the fuse is blown, a replacement will likely blow right away too. If you DO have the standby light, maybe the power switch (tact switch) is defective. While rare, I have seen these go bad in the past.
RE: no service manual. These units are considered “throw-away” units and are not repaired even under warranty, but replaced. Similar units that I have seen in the past, have either bad optics or bad power supply circuits. based upon the description above, I would suspect a bad component or two in the power supply.