What did you do the first time? If we know what kind of mixture you used and how you set it up, we might be better able to figure out what went wrong.
There are a lot of threads in the DIY section of the forum. If you do a search there, you'll see some good information (recipes, set-ups, etc.)
Good luck -- I just started up DIY CO2 myself and have found that it makes a big difference. My system is two 2-Liter soda bottles placed in a box to keep my cats from tipping them over. I drilled holes in the bottle caps slightly smaller than airline tubing, then used pliers to pull a 4-6" piece of tubing through each hole so it sticks down inside the bottle about 1".
I add 2 cups of sugar, 1/2 tsp of regular bread yeast (plan to try champagne yeast soon), and water up to where the curve of the bottle is just about to start (so I leave a few inches of headroom at the top in case it foams).
My system then is set up like this:
Each bottle with cap that has a few inches of tubing sticking out -> its own checkvalve -> a few more inches of tubing for each bottle-> T-Connector -> one piece of tubing that runs up the outside of my aquarium -> another check valve at the top -> tubing that runs down into the aquarium (held to the glass by suction cup airline tubing holders) -> limewood airstone placed under my filter intake, which is working pretty well so far
I change one bottle each week so that each bottle is running for 2 weeks. This keeps the CO2 pretty consistent, I've found.
Hope that helps.