macbookpro disconnects to airport when I close top

My Mac OS x Version 10.6.8. Pro 8.1 Memory 4mg.

Each time I close my laptop, or shut down it takes at least 12 tries to re-connect to airport. When I put in my router password it accepts it for a few seconds and then says 'timed out' and tells me it doesn't recognise my router no. There doesnt seem to be any consistent way of re-connecting. I have checked the router with a friends laptop and the bt router is operating perfectly. Sometimes I switch on laptop and it connects but most times it doesnt and I have to keep trying over and over again.

I am not very IT literate and not sure where to go or what to do to solve this problem. Is my Macbook broken? I would appreciate any help or advice.