You could either try inputting
hud_saytext "1"
in console and see if that does anything. If your console.txt is set to read only though, you'll have to turn the text file off read-only, then either open game and type that OR go into the text file itself and control-F for that line, see if it's a 0 (which means disabled) or 1 (which means on).
edit: If this doesn't help, and you have your console text file open, search for this line
hud_saytext_time "5"
That clarifies how long the chat lines stay up, if its set for 0, the latest update may have allowed that to completely remove chat. 5 is default.