The delete key failing is usually due to something going wrong with the configuration, for me it does not happen often, maybe two or three times in the last five years. the cure is normally, Tools menu - customise (or Tools menu - workspace - customise), in the options section of the dialog box, find the config you use from the drop-down box under the 'load from' button, and then click 'load from'. if you haven't done any customisation you can click the 'default' button if available.
This will reset many things in TC, and will normally restore the delete key.
Can I ask what type of TC you are using (deluxe or pro), and what version, (i.e v21 or 2016 etc.). This just makes it easier to target responses when there are differences between TC types/versions). many put the type and version in their signature, near the top of the forum is 'profile', and then under 'forum profile' one can add a signature which is displayed with every post.