Power went off during viewing. Nothing happens when manually using power button. Model # TH42PX60U. Could this also be a fuse issue?

It could be a fuse on the power board, as there are 2 or 3 likely on this model. If you want to inspect the fuses, I'd advise to do so only if you are comfortable opening up and repairing electronics, have a basic understanding of how plasma TV's work, and follow certain safety precautions such as unplugging and draining the power within the system.

If it is a fuse, replacing may not fix it or just cause the problem to reoccur, as typically fuses only blow when there is a short or over amperage drawn.

Some other troubleshooting tips, try unplugging the TV for half an hour or more and then replugging the TV in. Check to see if it powers on. Is there a click sound when you press the power button on the TV? Does the power indicator light turn orange, green, or blink? Can you hear any audio from the TV set at all?

Post back with your results.