EVERY kind of fish needs a filter and it's bad news if the filter packs up. The good bacteria that live in the filter need a constant flow of water or they will die off. In 12 hours they will have died off completely, the ammonia level in the water will rise and this will be dangerous for your fish.
So yes you do need a new filter pronto and you need to get some bactinettes or other refrigerated bacteria products (which contain good bacteria- don't get any other kind of good bacteria products that are not refrigerated because they don't work) and do plenty of water changes over the next few days.
Have you cleaned the filter out properly? I had mine for ages and was cleaning the piece of sponge inside (rinsing it out in ex-tank water to preserve bacteria [angelic emoticon]) but then it stopped working. I hadn't realised that the top bit of the pump came off as well and there was a little fan type thing in there which was so gunked up it had stopped turning. Once that was clean it started working again.
Thought that might help if like me, you never read the instruction leaflet in the first place .
Thanks pixel. I wil try that. I haven't cleaned the tank out thoroughly for ages as I was scared into not doing so by the fish shop man telling me that I'd alter the PH and kill all the good bacteria <quakes>. We have run water through the filter to keep the good bacteria happy and bubbled air in using a bicycle pump . Will get a new pump if neccessary at the weekend.
We don't have a good record TBH. All was well for ages until we introduced the sucking loach which massacred most of the goldfish of various types when we were away on holiday. It was grim . I spent ages trying to kill 'fin rot', clean the tank and add all kinds of bacterial preparations before we realised what the problem was. He doesn't touch the danio - too small I guess - but I won't get any more in case he does it again. Don't have the heart to get rid of the loach though.