speedo not working?

my speedo doesnt work at all on my vectra gls 2.0. the rev counter works and so does the fuel gauge and temp gauge.
the prev owner fitted blue leds ect and white clocks. without me stripping down the dash board, what could it be?
the display for the clock, temp gauge and radio doesnt work either. coule it be plugs or fuses?
please help as i need these fixed.
cheers