Keyboard function Key issues

Question

So my Keyboard on my Macbook has had some issues over the past 6 months, so about 6 months ago it started muting the sound on my computer when I pressed certain keys like : enter, esc, P, /, \, 0 or ) and a few others, to fix it though i need to hold down the mute button stops the other keys from muting my sound so I just keep a weight on it, since I'm a student and have barely any money. but lately after I finally updated my OS to maverick I found the Function keys option and clicked it, on, now it uses that App Expose function instead, so i can literally swap between muting and app expose. I've generally lived with it up until this point but I think I need to get it fixed, I doubt it is something i can fix at home but I just want to know what is happening before I spend my precious little money.

Answer 1

Sorry I left some stuff out. My keyboard has 2 sets of functions so when I UnCheck the Use 'F1, F2 etc keys as standard function keys' it switches to the Mute function on the F10 key, the decrease volume key on F11, etc so when it is on this certain keys will trigger the mute function without me actually pressing the mute key. Where as when I switch the 'F1, F2 etc keys as standard function keys' on those same keys that triggered mute now trigger         "app expose" function, so it doesn't help, also i didn't want to go into excruciating detail last time but some other keys either don't work like the mute key or the increase volume key and other keys do other keys functions. so in summary I probably should get the keyboard replaced but how long does that take? and how much does it cost