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The odds are the circuit board that your putting the fuse in is shorted out. I'm guessing that it's a power supply board.
Disconnect every set of wires going to the board. Put the new fuse in. Plug in the power supply board. If the fuse pops, then the power supply board is the problem and has a short somewhere. Most replacement board can be found at a good price at Shopjimmy.com or Ebay.com. Just make sure the part number on the board matches up.