Land Rover Repair: Land Rover wont start sometimes, land rover discovery, land rover discovery ii

Question
My 2000 Land Rover Discovery II will not start sometimes. I go to turn the key on the ignition and it seems as though the battery has died. I have a top of the line Optima battery that is no more than 1.5 years old. I have checked the fuses with an auto checker and I have found that some fuses under the driver's side fuse box do not light up when I press the checker to them. Fuses 3 LH Headlight Main Beam(Which is not working either despite brand new bulb); 18 Rear Wiper Motor(Does work); 23 Starter Motor; 24 Alternator, auto transmission; Fuse 35 Airbag SRS - Do Not Remove are non responsive when checked. I have checked all of the fuses and they seem fine, I have even replaced them with new ones and they are still unresponsive. I also found that one of the 40 V fuses under the hood's fuse box was blown and neither of the other two 40 V fuses responded either. Anytime that the car will not start I have to unplug one of the terminals on the battery completely and once again tighten it and then the car will start once again. What do you think the problem could be?

Answer
You say the problem changes when you remove and refit the cable.  Is the trouble in the cable itself?  They often corrode at the ends.  Failing that, you have to follow the power from the battery back to see where it's getting lost.  My feeling is, the trouble in in the vicinity of the battery cables