Problems connecting to the 'net

[KatherineB]

I have just bought an Asus ee Pad Slider, but for some reason it won't connect to the wireless router in the house. I know the password is correct, but I keep getting an 'Authentication problem' error message. I've googled a bit, but am not technically-minded enough to know how to follow some of the suggestions I've found. I do notice that, when it tries to connect, the signal strength, which has been good-very good, suddenly drops to poor. Can anyone help?

(Yes, I've turned it off and turned it on again, turned the wifi off and on, let it fully charge and tried again, and basically done everything I can think of.)