Acer Aspire 5050 - The wireless connection is turned off but there is no button to switch it on, can you tell me how to do it please? Thanks

Well There must be a switch on it. If You are pretty sure about this that its not there.
Than you can do one thing Look on the keyboard and observe the keys carefully you will find an icon on the keyboard look like an antena symbol look below:
Or Somewhat change on this icon. The default key on most keyboards is F2 or sometimes you need to hold down the Fn Key and they press the F2 Key