Everyone has mentioned the price, which could well be true, especially if you are competing with brand new houses in the same style which will have the full builders guarantee etc. (We had this issue with my mum's house).
Inside - I think it looks a bit dated. The wooden kitchen cabinets are not what most people are looking for in a modern house. The empty blue room could do with staging, and taking out the old fashioned things that remain in there. I would also repaint in a lighter colour if you can. Also repaint the purple wall in one of the other bedrooms, and change the purple and brown curtains for lighter, brighter ones.
Apart from that, it's a 3 bedroom house which you could reasonably expect to appeal to a young family, especially with that lovely open outlook and access to it, but the garden is just not child friendly so there is nowhere for young children to play safely with minimal supervision. I think that is the main thing that is putting people off.