Smells like a scam in the making.

I assume you have signed up and are ID verified for the new Managed Payments system?

As you are new, you will have to wait around 30 days once a buyer has paid to get the funds into your bank account. There is no more Paypal for sellers.

Did you make the laptop available within Australia only? I would definitely not be sending a laptop overseas - this sounds like a problem that will come back to bite you. If you did not intend to send overseas, then I'm sure you have not provided the correct postage, so even if the buyer was to pay, the postage would be too little.

Instead of waiting for the buyer to pay,  just cancel the sale (use "problem with buyers address" as the reason) and then relist it and block the buyer. If it was a Buy It Now item, you can tick the "Immediate Payment" required button, so that a buyer has no choice but to pay right away if they want it. Also, bear in mind that any sale over $750 must be sent with Signature on Delivery.

As @kopenhagen says, you are a magnet for scammers. You don't really know what you're doing and you're going to lose your laptop and your money. I don't think Ebay is the place to be selling these kinds of items anymore - there are just to many scammers out there.