No respone...nobody want to help me :(

There are free online repair guides for your 87 Prelude at www.autozone.com
that may cover at least some troubleshooting for this.

Also, try the free online repair guides for some of the Honda models listed
at
http://www.honda.co.uk/owner/workshopmanuals2.html.

It might take a bit of searching at the online manuals, but often there are
some step-by-step diagnostic procedures given.

speedo cable is either misalligned or worn.  replacement is the most
reliable fix although you may get lucky from a junkyard.  be very
careful taking the cable off at the gearbox end.  with some hondas, if
you don't do it right, the drive gear can drop into the gearbox, and
that's a world of hurt you want to stay /well/ away from.

Possible problems and solutions.

The cable connection behind the dash came loose. Solution: Reattach it.
The cable connection on the gearbox came loose. Solution: Reattach it.
The pulser or its driver is dead, which is unlikely. Replace it. The speedo
needle is miscalibrate, recalibrate it. The gauge's solder joints are oxidize,
redo it.