It sounds as though there's too much greenstuff in there - grass clippings? Add lots of shredded newspaper, cardboard as well - and some shovels of garden soil, too. If you can get hold of any horse manure, that's a great help. Then use your fork and mix it well. It might be easier to empty it onto a tarpaulin to do this. Hard work, but worth it.

When you get it back in, make sure that you 'balance' what you put in between green waste and other stuff - including tea and coffeee grounds!

This is a really good website about composting -
http://www.recyclenow.com/home_composting/index.html
It explains about the different ingredients you need to add to make great compost.

I think this FAQ from that website answers you - and it boils down to the same as Spritzhenry says.
http://www.recyclenow.com/home_composting/get_advice/making_compost_faqs/our_compost_looks.html