I bought the full game with my family's pc, at my house. It worked, Audiosurf appeared in the steam "my games" instantly, no problems.
When I returned to my own flat, in student halls, (where I have used and installed steam games before, so I know that steam itself works) Audiosurf was not in the "my games" tab on steam, and the only options on the "store" tab were to buy the game again, or to download the demo.
So I thought, ok, it's being screwy, I've read about stuff similar to this in the audiosurf forums.
I restarted steam, still not there.
I then installed the demo version, which added 2 entries to the "my games" tab. One was for "Audiosurf demo", which I played successfully until my allowance for songs had run out. The other was for "Audiosurf", and under "status" for the entry, it says "Preload Complete".
I restarted steam while the demo was installed, but I was still stuck with "preload complete" for the full version.
So I right-clicked --> "delete local content" on the entry "audiosurf demo", which removed both audiosurf entries from the "my games" tab.
I'm reinstalling the demo again, and it's appearing to be exactly the same as before.
I'm definitely sure that it was bought on the same steam account (ScottyMcNoob), and the money's been taken out of my bank account.
Can anyone help?