Have you corresponded with this seller letting them know that you are not happy with this trade? I think PayPal/ebay requires you to allow the seller to try and make good on the transaction first.
Then if they don't, you have the right (and should) contact PayPal for reimbursement.
Even if Dad is incapacitated, he still has a responsibility to his sellers. So yes, do follow through to either get a working machine or a refund.