[Donnay]

Hi

I am trying to grow melons this year in my greenhouse. They were doing great and all of a sudden all the flowers are falling off and the fruit behind is dead.

The plants are looking fine, really green stem, leaves and looking healthy. I can't see any mites etc on the plants and they are not under or over watered.

Can anyone help me please, do I need to be worried??

[mumofstig]

They need warmth (don't we all) and they need pollination.
If you close the windows and doors to keep things warm - then the insects can't get in for pollination. Perhaps some hand pollinating would help 

[Donnay]

How do I do that? Sorry I'm a newbi!

[mumofstig]

The male flowers are just on a stalk, but the female flowers have a little round bump of a fruit behind the flower.
Assuming you have both kinds of flowers (sometimes they get out of sync for a while - but will sort themselves out)
http://www.gardeningknowhow.com/edible/fruits/melons/hand-pollinating-melons.htm