I made the mistake of working on a light switch live, a hot wire touched the switch for the fan and sparked and now half the room has no power, it did not blow a breaker. What needs fixed?
Presuming the half of the room that does work is on the same breaker as the half that doesn't, then you would need to start by testing for power between what works and what doesn't. If we're talking light fixtures that aren't working you'll typically find power from the thick wires, but that the light fixture's little wires are burnt or blown apart (exploded) and hopefully just that fixture needs replacing...you'd replace the outlet, if we're talking wall outlets.
If or when you find a light fixture with ruined wires, you can connect the thick wire sets together to see if the rest of the run works from that point, the same bypassing goes for outlets. If, nothing works and you're not reading power from any wires, then you'd need to re-wire between what works and what doesn't. Repeat this as needed until everything works again.
In most older or renovation situations, you can pull a new cable with the old cable from fixture/outlet to fixture/outlet, the benefit of most daisy-chain installations. For newer and proper installations, you'll need to remove the wall or ceiling box at each fixture/outlet to free the wires from nearby staples.