Receivers and Audio Components

I just bought the receiever off ebay, it was refurbished, but I picked it up for about 110 bucks. It works fine, other than the left front speaker not working. Does anyone know if I would be able to go in there and fix it myself? Im pretty good with this type of stuff, but never attempted this before, so I dont know what kind of tools I would need. If its not a DIY project, does anyone know how much it would cost to fix?

PS its not the speaker and its not the wire, or anything like that, Ive tried that, and I wish it was that. 

I have the crossover on my sub set to 120 and the crossover in my receiver set at 80. My main speakers have a response of 120-23,000. My question is - if the sub will not reproduce anything above 80 and my main speakers will not reproduce anything below 120 - where does the freq between 80 and 120 go? Any help to this would be appreciated.

I've noticed recently that first thing when I switch my hi-fi system on, the right speaker is either silent or very quiet. It seems to turn on after a minute or so, but obviously I am concerned something is dying and eventually the speaker won't work at all!

Firstly, what's the problem likely to be? Is it more likely to lie with the speaker itself, or the amp unit? Secondly, I extended the cables a few months ago - could it be a bad connection between the old and new wires?