Cuore- Electrical Problem


I have a 1998 997(?)cl Cuore and i fitted which i presumed was a recharged battery, however upon installing this i recieved a puff of smoke coming of the fuse box under the car bonnet which i have change a single 30amp fuse which was blown. I have since bought another Sad new battery and the car knows i have electric as the use of hazards and side lights are working but i get no engine lights or engine start. Is there a logical/quick/cheap fix or am I looking at a right git to solve?