The bonus multipliers are all on the same circuit board under the playfield. Try wiggling the connector on that board with the power on (be careful!) to see if the bulbs light up. You can also try disconnecting / reconnecting it but it's common for the pins on the board to have broken solder joints. It's usually a quick and easy fix to add a little solder to the pins and you're good to go.
For the backbox GI, check the long skinny board in the bottom of the backbox. One of the connectors on the right side below the fuses will probably be a little burnt. You will need to replace the connector and pins in order to get the GI properly working again.
In both cases, a basic multimeter will help you determine if you're getting power and can check for continuity if you have a broken wire somewhere.