It often helps if more info is given.. PC spec, screen type... As the likes of Jim are having to guess which leads to allot of work for him... the more info you can give (within reason)
can only help..
On a desktop PC with an ATi Radeon 5770 1GB GDDR5 graphics card, connected to an old TV with a HDMI cable. Screen resolution is 1920x1080. CPU is an Intel Core i5 750 @ 2.67 GHz, 4GB DDR3 RAM
Ah that's a good point! It's a HD ready TV, so 720p. So I guess that's why it won't let me change the resolution. Although every other game I've played with this monitor (Dirt 3, Race series, F1 2011) allows me to change the resolution to 1920x1080. I'm confused!
There's a similar post on the Steam Discussion area and he was able to fix it by messing with the settings on the TV, something to do with scaling mode? Not too familiar with any of that stuff.
I had a messed up issue once and I had to change to windowed mode to change the resolution, then went back to regular and I could choose everything again....odd.