This is what I would do:
Join a group (eg slimming world- super easy, eat loads, great support)
Set smaller interim goals...a stone at a time should be good.
Imagine how you will look once you've lost all the weight.
Think of the health risks of being overweight.
Think of the clothes you'll be able to buy when you've lost the weight.
Come to this website often.
I have tried all sorts of different diets, and also the old fashioned eat well and exercise way. The one thing I know is DEFINITELY working for me is slimming world. Its so so so easy, you get heaps of support, you can eat loads if you want to and still lose weight and its good for introducing exercise, though this is not a requirment of the plan - just an extra. Go for SW, you won't regret it! I have lost 15lbs in 6 weeks, and thats with a few takeaways and crisps lol.