Latitude D630, Windows 8.1 - WiFi not always working

I've just added an SSD to my Latitude D630, and also put Windows 8.1 64-bit on it (still in evaluation mode). Ultimately, the intention is to move to Windows 10, but I can't do that until I actually purchase Windows 8.1.

When I start up, Wifi sometimes works and sometimes doesn't - maybe about 50-50. When it doesn't work, I can get it working by going into Network Connections and disabling - re-enabling WiFi.

I've updated the BIOS to A19. I can't install any of the Dell drivers for D630, as they don't support Windows 8. Device Manager indicates "Intel(R) Wireless WiFi Link 4965AGN" for the name of the network adapter, and driver version 13.3.0.137.

Any idea why this might be happening, and what I could do about it?

Thanks - Calum