Proteus 8 Simulation Errors. Loaded Netlist?
This is because you are using a logic toggle part. This cannot provide any current in the simulation, it is literally a logic level.

If you go to the debugging tools section on the parts list (where you got the logic toggle part from) you can also select a logic level indicator, which will go to a 1 or a 0 depending on logic level.

For an LED to work, you would need to set it up as a real circuit, with a voltage input, switches and resistors.



The logic toggle and logic indicator parts are to be used to check that logic levels are only supposed to be used to verify a logic circuit is doing what it should be. Once it is, you would have to turn it into a real circuit to get LEDs lit.