Afterburners use reactor energy to work. Next time you use it, look at your energy bar... when its empty the afterburner should stop working. If you have a weak reactor with a strong shield the afterburner will barely work.
The tarsus sucks completely and fighting even talons is hard in it. Let me give you the right picture... the tarsus is the slowest ship you can have, its the less maneurable ship you can have, its the most undergunned ship you can have, its the ship with less armor you can have and its also the ship with less shields you can have, there is absolutely nothing that the tarsus does well. You have to do plenty of easy missions and trading between the bases in gemini and buy a better ship. Keep in mind that not all ships are meant as military fighters either... if you plan on doing serious fighting I advise you buy a orion or a centurion, if you want to do serious trading you have to go for the galaxy.
I wish I could somehow help you too Fatcat.. but I have no clue of what happened with your game, sorry.