It's hard to say -- as Gazander said, you can test the batteries to see if they are up to voltage. Many inexpensive volt/ohm meters have testing positions for different battery cells, and may be a handy thing to have. If you don't have one, you can go to Radio Shack and they'll test them for you (just don't listen if they tell you that the batteries aren't any good and you have to buy a basket full of their batteries as a replacement :-)).
It could be that your charger is fried or defective. One of the reasons that I went ahead and popped for the Maha C401, even though it's a bit pricey, is that it's recognized by many as one of the best chargers of its type available. Instead of either one circuit for all four batteries, or two as is very common, it has a separate circuit for each of the four batteries. and a separate light which turns green when each cell reaches full charge. It might just be a marketing gimmick, but I have reasonable confidence that each of my batteries is fully charged when I take it out of my charger. It's important for me to have that confidence, and since it's not let me down so far. . .