This is strange.

[gozpel]

Yesterday, I noticed a Steam-patch going through and today Civ5 won't open.

It goes as far as to choose DX9, then an error report comes up and I have to close it all?

I never really had any big issues with Steam, I just need to know where to start to look for some reasons so I can sort it out.

 

[komodo87]

It's happened to me before I fixed the problem by uninstalling the game then installing it again.

First go to your steam library, right click on CiV, go to properties, click on the 'local files' tab then 'verify integrity of game cache'. If this doesn't work unistall the game then install it again, it worked for me.

 

[gozpel]

Thanks komodo87, the "cache-thing" did it!