If the speed info is coming from the abs then this computer will need to be check first if its ok , and all the other stuff is working on the instrument panel then the wiring will need checking from the abs to the panel and if that is ok ,you will need to have the signal,checked which goes to the panel while driving to see what is at fault and if the signal is still present when the speedo drops to zero, new panel required,hope this helps.
mark
October 2008