IPod charges on computer but not on genuine mains charger
I recently aquired a used IPod mini 1st generation 2 gig from a friend. The unit was flat when I got it so I plugged it into the genuine Apple mains charger and firewire lead which came with it and got nothing, not even after leaving it plugged in for about 6 hours. So I then plugged it into my computer usb port with a non Apple lead and bingo, the battery began to charge. I left it plugged in most of the day and this resurrected the IPod. However, when I plug the IPod into the mains charger, it does not charge still, it will only charge via my computers usb or firewire port. I thought the charger may be faulty, so I used a non Apple mains charger from my 4th gen IPod and still no charge. I know both chargers work o.k. as they charge my 4th gen perfectly. Any ideas please?
Dell Windows XP Pro