Wireless connection problem

I have accessed my BT broadband connection on my laptop via a D-Link
wireless router for several months withe no problem whatsoever.

However, since about 5 days ago, the wireless connection does not connect
to my network automatically when I switch on the laptop (as it used to do).
Now I have to "repair" the connection several times before it eventually
connects (approx half an hour every time).

It's not as though the wireless card does not see the network straight away
- it does as it shows up under "View Available Networks", and has an
excellent signal - it just won't connect for some reason.

I've run Ad-Aware, Spybot, and Symantec AntiVirus but everything seems
fine.

Anyone any clues?

mrb