Nba Gametime Pro's power switch is located on the back left side of the game, the "I" should be depressed.
To activate the game you have to hold the start button down. When pressing the button you should hear a faint click inside of the control panel. If you are hearing the click check the harness below the control panel is fully plugged. You can remove it by squeezing the locking tab on the long side of the connector and pulling away from the control panel, check for loose pins and then reinsert the connector to the socket you should hear a click when the connector is fully inserted.
There is a power supply that is located in the electronics panel on the back of the game. When the unit is plugged into the wall and turned on there will be a red or green light on the power supply regardless if the game is active or in sleep mode. If there is no light then the power mod fuse could be blown or the power supply is bad and will need to be replaced. The ICE part number for the power supply is UC2010