Landlord duties - I need a new window!?

I have lived in my rented property for 3 years now, for 2 of those years, after suffering from horrendous winters, I have constantly asked for a new window, it is rotten and won't be long before it jumps off itself in protest, what do I do to get the landlord to get off his fat lazy backside and get this job done? I'm thinking of getting it done myself and then telling him to take it out of my rent (whatever the cost?) any ideas anyone? I'm dreading another winter - I love the house and don't want to leave it just because of the window when it could be easily sorted. (I'm not late with any rent payments and haven't been, I'm no trouble, keep myself to myself and respect the neighbours yet I'm treated like this??)