Does the battery have a manufactured date on it?
If it's +10 years old then it may well be worn out and you'll need to fit a new one, especially if it's suddenly gone.
Alternatively, if it's gone over a longer period then think about anything you've done in the past few months. Fitted a new stereo maybe? These things can drain batteries over time.
Let us know a bit more about the situation and we can help a bit more.
Alternatively, it IS a 1.4 Golf3. A flat battery is an excellent reason to scrap it....