Bluetooth Keyboard doesn't pair properly with macbook pro

I have a late 2010 macbook pro and bought a apple wireless keyboard the same year. i used it a lot with a apple wireless mouse, i havent used both in about 3 months and started to need to use it again.
My mouse connected perfectly but when i try to connect my keyboard a message pops up saying i have to enter a password on the keyboard to fully pair them but the usual blue glow that appears around the number you have to type doesn't appear and a sentence pops up immediately saying finalising the device then the pop up disappears.
i am unable to use the keyboard and the pop up pops up again. i have new batteries in it and it works on my brothers laptop. i used his keyboard and it worked and first bu now that also does the same?? really confused and my both laptop and keyboard have just ran out of warranty cheers