Check the on/off switch for continuity. But you may simply have a secondary fault somewhere. I recently put a scope on my project to do a line-up, and the thing died on me. Turned out to be a paper cap, nowhere near where I had attached the probe, which had gone shorted on me. DC resistance 350 ohms instead of infinity, and it had pulled the PSU power output down to almost zero. I replaced it and the thing was live again. The scope probe was purely coincidental.
