We have a desk top PC using a Netgear wireless router and my wife has a laptop with Wifi enabled. It has been OK until recently when it started to fail getting connected on the odd occasion, but now it will not connect at all, any ideas?

Try changing the wireless channel?

Yep change channel, it may be that someone else near by is on the same channel but just causing interference. Perhaps they have added a new device or someone else has also set up a wireless network on the same channel too (espesh given its xmass).

I've had to do this 4 times now to get a decent channel.

I agree with ^ . Someone nearby may have installed a wireless system and be grabbing the default channel. Happened to my neice. It was intermittent and that confused me for a while. It all depended on who switched there router on first.

How do I change channels?

Depends on your router, should be an option in the wireless settings on the web admin page.

I had this problem with a recent new laptop added to my netgear router,i really didnt want to go through the painfull helpline but they did actually sort the problem in the end.

A firmware update from the netgear site was downloaded and all is well now,not saying this is your cure but the call was worth it in the end.