Problems connecting to SKY Wireless Router

[The Mad Rapper]

I am trying to connect on a Dell laptop and can see the router in the available wireless networks, but when I try and connect and am asked for the network key it throws up an error message saying that the key can either be 5 or (a higher number I can't recall) number of characters. The network key SKY have provided just keeps throwing up that error message - any idea why?

My sisters PC connects wirelessly upstairs without a problem, so I have no idea why this laptop's kicking up a fuss. I am hoping it's something simple!