If you find you are unable to select markets in Guardian properly and your market list now has unfamiliar fonts for the column headers similar to the image below then that would suggest the current layout profile you are using has become corrupted.
This is something that is quite rare however very easy to resolve, all you need to do is logout of Bet Angel then log back in again - using the factory default profiles on the blue login window.
Once logged in you need to delete the offending layout profile you were using, to do this on your main Bet Angel screen in the upper left corner of your screen click;
View > Delete Screen Layout (and select the layout profile to be deleted)
You'll then need to recreate and save it or if you already have a similar layout profile saved you can select that to start with and make the edits required before saving as a new layout profile 'Save AS' a new layout profile