I've just taken a look at the Steam website. Every game I've viewed has a 'System Requirements' section, showing the relevant graphics requirements.
Apart from things like simple card games, etc, hardly any modern computer games will run on a 'bog standard' PC. (They're designed for office use). You nearly always need to install a graphics card before you can play games, with many of them now needing 3D cards.
If you've genuinely been misled by the Steam website (because, for example, the site shows incorrect information about the relevant graphics requirements) then, irrespective of any limitations which might appear to be imposed by the company's T&Cs, you have the right to a refund because the goods you received were not 'as described' or 'fit for purpose'.