Not sure if anyone has the answer to this.

I have a Sony laptop and over the last couple of months, the '-' key (right of the 0 key) has stopped working when I press it, but will often start working when I don't want it to, i.e. when I'm on the internet, typing a word document, or anything requiring written text, such that all I get is; ----------------------------------......

It is extremely frustrating. I haven't spilt anything on the key and wonder if its not a software problem?

Any thoughts anybody?

You do not have to spill anything on a keyboard for it to get gummed up. Dust, dirt, hair, dander, critters that eat dander, waste products from those critters, and smoke particles in the air all conspire to ruin our day - in our keyboards, and inside our PCs (creating blankets of heat trapping crud).

Ensuring the power is off, get a toothpick or some other non-metallic, thin but sturdy probing tool and carefully dig around between all the keys. You will be surprised and disgusted at what you can dig out. Then get a can of compressed air (Radio Shack, Home Depot, BestBuy) and while tilting the keyboard and pressing on the various keys, blast away in, around and under the keys. Tilting the keyboard helps prevent having to tilt the can of air so much that super cold liquefied air is spewed about.

If that does not work, you will have to result to more radical cleaning measures such as used in these tutorials:

Keyboard Cleanliness

Cleaning Laptop Keyboard

If you are uncomfortable with the more radical approach, take it to a shop.