WR250F speedo problem

alright people ? just joined hope you can help me out with a wee problem i have? ive got a 2004 wr250f. i was out on the bike today doing some offroading . then went back to the normal roads. everything was fine . but after 20mins on the road the speedo just died. everything else is working lights etc, just don`t know how fast im going. can anyone shed some light on this for me.

thanks in advance , steve

ps- here`s a wee picture of ma bike