By no longer work, you mean don't turn on, correct? Is this on all lots or for just one particular household? If it's just one household, there's a few possibilities:
- Unpaid bills - If your electricity was shut off due to unpaid bills, you won't be able to turn the lights back on unless your Sim pays (or the repo man takes your stuff to cover it)
- Call from Landgraab power company about squirrels - if your power was supposed to be shut off for only a day or two, but never came back on, try replacing the mailbox.
- Power Conservation NAP - again, this is only supposed to be for one day each week, but if it gets stuck for longer, maybe try replacing the mailbox? I would also send your sim to get signatures to repeal the NAP
- Off the grid - if you have the off the grid lot challenge on, you'll either need to use the off-the-grid lights or get solar panels or a generator (or remove the challenge)