The deal never said anything about responding to your messages did it? He may have sold the item and posted it just before taking off on holidays for a fortnight. Who knows? You have plenty of time to file a claim. For anyone to really give you the advice you seek we would need a whole lot more information.
Some people, not saying you in particular, make ebay transactions a pain because they are too demanding and or impatient. You pay for an item straight away doesn't mean it should arrive within a week. When I read threads like this I think of highly strung or drug affected people freaking out, before enough time has passed to warrant worry.
You say you have bought from this same seller and had another issue. Then that should have been a signal. You should have remembered and not chosen to bid. It hasn't been seven days and you are wanting to start a dispute procedure at the earliest opportunity. Settle down. Is Rabies still running rampant over there? You have 45 days with Paypal and a further 45 days with your credit provider, if you happened to use one on this transaction. Without enough background information I shouldn't be so harsh, but until I do have it, maybe I should be harsher.