Hi Marg,
If you place mouse flat on you desk and look closely, you will see a tiny arrow pointing towards you in the middle just between and below left & right keys. iF GOOD FINGER NAILS ( IF NOT USE TINY SCREWDRIVER) SLOT IN NICK JUST ABOVE AND PULL TOWARDS YOURSELF, IT IS A BIT FIDDLEY BUT EVENTUALLY THE TOP WILL COME OFF LEAVING GAPS EITHER SIDE OF THE BUTTONS LEAVING A CHICKEN WISHBONE SHAPE PLASTIC TOP IN YOUR HAND. YOU WILL THEN SEE WHERE THEY GO, EVEN MARKED PLUS & MINUS FOR YOU. GOOD LUCK HOPE THIS HELPS. HAD SAME PROBLEM MYSELF THIS AFTERNOON.
REGRADS KEITH
Sorry about the capitals got carried away.
Keith, January 2009