Are both VGA outputs on the SAME graphics card?
If one is on a card, and the other on the motherboard then it very likely can't work as it's usually the addon card OR the motherboard output.
Even if you could SPLIT the signal from the same VGA output without signal degradation, you'd just get the same image on both screens. So you need TWO outputs, usually from the SAME card.
If needed however, you can add an inexpensive card like an HD5450 just to drive the 2nd monitor though I'd get a 512MB model if using 32-bit Windows.
Many video cards have a VGA output as well as the option for a 2nd VGA output via an adapter (for DVI-I, not DVI-D).