Pressing start does nothing.

Game will not start: first checks

Cause: Most often something simple: no power, no credits, a missing ball, an unplugged connector or a fuse.

Checks

• Check that the game is plugged in, the outlet is live and the game switch is on.
• Check there are credits or free play is set.
• On solid-state games that need several balls, make sure all are installed (a label under the lockdown bar or the manual gives the count).
• If you just moved or worked on the game, recheck every connector and the wiring you touched.
• Test the fuses and fuse clips.
• Check the start button switch closes and its wires are intact, and that the coin door connector is plugged in.

Fix

• Correct whatever check fails.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7
• Williams System 9
• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C
• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95
• Bally MPU AS-2518-17
• Bally MPU AS-2518-35
• Stern MPU-100
• Stern MPU-200
• Bally 6803
• Gottlieb System 1
• Gottlieb System 80
• Gottlieb System 80A
• Gottlieb System 80B
• Gottlieb System 3
• Data East CPU Version 1/2
• Data East CPU Version 3
• Data East/Sega CPU Version 3b
• Capcom
• Electro-mechanical

Source: Pinball Machine Care & Maintenance, Bernard B. Kamoroff (Bell Springs Pinball Alley)