After a clear you must use the SET chip to enable the bill validator or it will not accept bills. Directions on how to use it can be found here:
http://www.newlifegames.net/spset/dbv.htmAssuming you're hearing any sounds, such as the ding of a coin-in or win, the following applies:
I can't quite read the label on the picture of your MPU board. Is that SP1271? I have attached the PSR for SP1271, and also Ron (R273)'s "for rookies" spreadsheet which helps to make it easier to navigate the PSRs. It looks like on the 1271 the sound option is page 0, option 2. Change the option to whatever it isn't currently set to.
If you are not hearing ANY sounds at any time, check the volume control (blue dial on the MPU board which can be accessed even when the board is installed). You may also need to ensure that the wiring to the speaker hasn't been cut or otherwise disconnected. The speaker should be located near the lower left corner of the door as you look at the machine with the door closed.