So does the following not show up for you: μῆνιν ἄειδε θεά
Some of the older posts on this forum got their Greek characters scrambled, but you should be able to see the Greek in the newer posts. Do you see polytonic Greek on other sites, though? The site in the picture is only using monotonic Greek.
For Perseus, the only thing I can think of is to make sure you've set your display preferences to unicode. Otherwise you would need the specific fonts to see the Greek.