New battery won't charge - PRAM capacitor problem?

Your old battery is dead and gone - but the new one refuses to charge. A good many times a defective PRAM capacitor (the blue round one in the middle of the picture) might be the cause. It is located near the red power and reset buttons and is used to keep the date and time for a short while when the battery is changed. When it is not longer working it disturbs the charging process.
The PRAM capacitor has 5.5V and 0.33F - you'll find it in (web)shops of consumer electronics retailer for 4$ or less.