my copy of FE:LH refuses to launch altogether. Steam is giving me the error "failed to start game (app already running)". The game is not already running (this error happens consistently, even after a fresh boot of the computer). As there is another game on my Steam installation, which launches normally, I suspect that this is a FE:LH error and not a Steam error.
I tried removing my local files (saves + mods); verifying integrity of local files with Steam; full reinstallation of the game with Steam (delete local content + install game). This changes nothing at all: same error, "app already running". I did not see a known fix for this problem on this forum, either.
EDIT: OS is Windows 8. There are almost no other programs running (I barely use this computer under Windows, except for a few games).
How should I proceed to make the game run again?