Don't want to seem like I think you're incapable, but be absolutely sure the battery is charged, by a simple test:
Turn the headlights on full, in high-beam mode, and then try to start the car. If the headlights are dimming a lot, it is a voltage-related problem, possibly battery. Otherwise, it may well be the starter.
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black