Oh yes, did I forget to mention that the board has been changed.......? Sorry thought that would have been fairly obvious!
To be fair, you DID say you were upgrading to an i7. Nothing was mentioned about a new board. I'm sure a 1366 socket CPU has been attempted to be forced into a 775 socket board. We like to make sure. Normally I would assume, but with the large amount of uninformed people, you can never be too sure.
I would recommend you contact the maker of your PC. I'm sure Alienware owes you some help with the price you paid for your system.
I hate to say this, but that WC setup can probably only cool about 125 watts max. it's only a 120x1 rad and a pretty weak pump/block setup.
Don't think it will cool a 250 watt CPU very well. Might want to reconsider your options. Might need to start over if you stay water, here is our guide on Toms, and look at the other guides link in this.