windows and sun roof are operated from becm under seat . most likely the window switch pack has lost power , not related to becm remove switch pack and check power at board most likely has corrosion on it first place to start IMO.
BECM is under the Front/Right seat... but if all of the windows/sunroof are dead - also check the electric adjustment of the mirrors. If they don't work either, then chances are your issue is actually the window switchpack (which happens to be right under the sunroof) rather than the BECM.
If you are in the UK, then I do refurbished window switchpacks on my website - if you aren't in the UK, well, I will ship internationally, but it might be cheaper to find one from a parts website/dealer nearer.
But for my money it's the switchpack that's faulty, not the BECM. If it were the BECM that had got moisture in it then you would have a load more electrical headaches than just windows/sunroof.