Wifi connectivity with intel 5100 AGN

I have a Sony Vaio with intel 5100 AGN wireless adapter & Vista OS.

The problem I have is that 9 times out of 10 it will not connect to my home or office wireless network. Eventually it does, though only after switching the adapter on and off several times or rebooting the machine. Sometimes I also have to restart the wireless router.

It will always seem to connect in that I get the connected icon in the notification area (though often without the internet globe symbol) though it will not connect to the net or to any other machine or printer on the network.

Some other useful info:
Both the home and office routers are the same model (Comtrend) and both work fine with other PC's

I often have bluetooth problems also - can take a while for bluetooth to start (I use a bluetooth mouse) and I have 3 unknown bluetooth peripheral devices in device manager

I have McAfee internet security installed

I have tried:
Disabling the firewall
Removing and readding the wireless and bluetooth devices
Disabling IPv6
Driver & OS update
A clean install

Nothing has resoved this issue which is becoming a pain as I can now spend up to half an hour each time trying to connect.

Any help is very much appreciated.