Whenever I press the shortcut keys Ctrl+Alt+T for LXTerminal, a blank terminal window flashes and disappears.
I had the same problem. I merely renamed my ~/.config file to .config.bak and then logged out. The resulting creation of the new .config file enabled the use of Ctrl+Alt+t to open the default terminal. Warning however: All configurations that you had previously created will also be eliminated so if you have spent time creating them. You may just want to live with launching the terminal in some other manner such as via the menu or with Run. Your choice.