Umm have you checked the fuses in the boot? There is one there that controls the tail lights and the dash cluster light (yep 1 fuse for those 2 things, wierd).... just replace it, and it should be fine, they may have shorted something accidentally when installing, it's not a big deal, i've done the same thing when removing my dash once... It's pretty common. Obviously if you replace the fuse and it blows again, then there is something wrong with the wiring that needs to be checked..