Computer seems to think game uninstalled?

[Diggun]

Anyone else had this? I normally launch from a desktop shortcut, just fired up the computer, click on shortcut and instead of running the game, I get a steam pop up saying I'm about to install it. Steam also seems to think the game is not installed when I open it there. But all the files are where they should be, and it was running fine last night and I haven't deinstalled anything! I'm probably missing something super obvious. Any ideas? 

[szelljr]

Try this: Properties-Local Files -Verify Integrity Of Game Files