Problem connecting to Netgear DG834GT with Windows 7

I am having problem reconnecting my wife's laptop by wireless to Sky router/modem after spell using it abroad.I can see the correct access point but laptop will not connect. I use WA-PSK and network key has been double checked.SSID is broadcast and mode is g&b.
Strangely when I connect to modem by LAN cable it the network sharing on laptop shows that it is connected both by LAN and wireless. When LAN cable removed laptop remains connected by wireless for short period before losing all connectivity. MAC access control is not enabled and strangely there appears to be a different MAC address showing for laptop compared to previous when it did connect .Any ideas welcome please

While first making sure you software firewall is switched on on all the computers on the network, try the laptop with the wireless security turned off.

I've seen PC's get stuck in this state, and a reboot resolve it, and then work for an hour or two and then fail again. So worth checking that the computers wireless card does not have a firmware update available