For most tables, Press the top 5 key on the keyboard for credits and the 1 key to start the game. Don't use the NUMPAD 5 and 1 keys. They won't work.
Some tables start by pressing the 's' key, others by pressing the 2 key.
If you download a VPinMame table, you need to download two files (1) the .vpt table file. Unzip it to the Tables folder, and (2) the specific PinMame ROM file for the table. Download it to the vpinmame\Roms folder and KEEP IT ZIPPED.
Not all tables are VPinMame tables. Most Visual Pinball-Only tables use no additional files, though a few do, like additional .mp3 files that go to the Music folder. Only VPinMame tables use the PinMame ROMS. These are recreations of actual machines using the same software (the ROM from the machine) to recreate the game behavior, sounds and videos in the DMD.
You will know that you are trying to play a VPinMame table because when you start a VPinMame table by clicking the Play arrow button in the Visual Pinball editor, you will either see the VPinMame Splash Screen with the name of the table at the bottom, or you will receive an error when things are not right yet, like VPinMame cannot find the ROM.zip file in the Roms folder (when the correct file is not there).
If you are starting a VPinMame table for the first time and in the DMD (the ScoreBoard mini-screen in the upper Left corner of the Screen) you see the FACTORY SETTINGS RESTORED message, then press the top 7 key and wait a moment for the table to reset to Play Mode.
If nothing happens after a few moments, then press the F3 key to reset to Play Mode. This is because different machines have different routines the first time they are turned on, and VPinMame recreates this behavior.
After it resets in a blink or within 30 seconds, you will see a score in the DMD, then press the 5 and 1 keys to start the game.