Wireless keeps disconnecting

We have a Netgear wireless router and a laptop which we bought in 2004. To enable a wireless connection we need to press a button at the top of my keyboard every time the computer restarts. We haven't had wireless set up in our house for very long, and on our newer laptop (which we purchased this Christmas) everything works perfectly and we use an on-off switch which only needs to be turned on once. However, in the last week on so, on the older computer, the wireless connection keeps cutting off every five minutes or round about. The problem is solved by pressing the wirelss button twice to disable and enable it again, but this is annoying as the connection often cuts off during downloads or important page loads etc.

I'm wondering what is causing this and if anyone could please help us to solve the problem. I'm not sure, but I'm wondering if this issue started when I set up a WEP key on the connection. Could there be a link as I don't want to compromise security if it won't solve the problem anyway?

Thanks.

Cathy