[NoOne]

typically < alt-enter > will toggle full-screen and windowed mode in an application.. if that doesn't work you need the Settings from the main ootp screen after it loads up -- just as yawgmoth mentioned.

what's resolution of 40" tv? 720p? 1080p? match native reso for best rendering. 4k? even better, although if you aren't near your tv, you may want 1080p for more easily read text relative to distance from tv.

if it's 720p, that's 1280*720. It likely can also do 1080i but i do not advise it. interlaced videos looks like crap. even though it has more lines of resolution, technicallly speaking, 1080i looks worse than 720p.

it could be windows just defaulting to something when attached to a new display, if the tv is not the normal monitor. may just need a simple disply settings change in windows and it will all fix itself after that.

belated edit:

tip: turn off any processing done by the tv on the image. it can cause input lag. so, turn off mpeg noise reduction, turn off all that type of stuff. if there's a "game mode" on that tv, it will do that for you. otherwise, you'll move the mouse or type on your keyboard and there will be a delay between what you do and what you see on the screen... sometimes to drastic effect, other times not so much.