Strange VID-AR587 Problem when fitted to card

[speckled]

Hi I was wondering if anyone can help with a strange problem when I fit a waterblock to my HD5870, basically I purchased a second card and waterblock to run HD5870 in crossfire. The strange thing is the card works as expected when stock cooler is fitted but the card then stops working when I fit the waterblock and add it to my loop, I have had it on and off several times making sure it is fitted properly and also fitted new TIM pads to the block and made sure proper contact with all components to be cooled.
This is driving me up the wall as it makes no sense at all, any help would be greatly appreciated.

[Izerous]

This may not be noticeable on the TIM pads but parts of the block may be contacting parts that it shouldn't. I would go around making the the block isn't touching in any extra places.

[Ace0751]

Also make sure the pads are the correct length with the spots that need padding anything shorter than its length may be touching with the block causing it to mess up. Make sure their are no rips with the padding wither.