Sounds like your switch is broken..This is a very small delicate surface mounted switch so good eyes are needed..You can buy old broken motherboards from ebay for just a few pounds and although rather fiddly you can replace the switch in just a few miuntes.Infact if you remove the bottom and locate the switch you can also desolder the small tin cover which is only soldered on each side.Carefully remove the cover and you can now replace the inside of the switch without even removing it.Be careful of the small spring inside..
Alan stephens., October 2008