You can always check if there is something wrong with the flash light itself by testing it with the lightning button (4). Pressing the button should trigger a flash. If it doesn't - and the little LCD screen is on - then you should check the flash bulb as it's probably broken.

If the LCD screen is off, it's more likely a power issue. Follow the steps below.

First always check if the power cable is connected tightly in the Power socket (1) of the flash light, it can come a bit loose over time. When this is not the case, follow the power cable and check the other end where it connects to the Capture Tower.
If these connections are okay, but the flashes won't turn on AND the Capture Tower tablets and camera work fine, it's either internal cabling or the fuse.

It may occur that your fuse (14) will blow (to protect the rest of the hardware) and that it needs replacement. To put in a new fuse, you must disconnect the power cable from the Flash light and push the fuse holder out with a small screwdriver.

In the fuse holder you will see that there is a spare fuse which you can use immediately. Make sure you replace the broken with the spare, and the spare with another spare from your spare kit!

As a rule of thumb, none of the icons in the top row should be visible. You can turn them off with the numbers given on this image:

Remove the adapter on top of the camera and put it back (if possible, some models have shrink wrap around this part, making this unnecessary). Also check all cables that lead from that point, disconnecting and re-connecting them at every possible point.

As a last resort, you can reset your Flash light. Reset the Flash light by pressing 6 and 8 at the same time. Then disabling all options as described above.