Dimmer circuit not working?

We have a double ganger light dimmer and after many years one of the lights, a 300w halogen would only come on intermittantly. We changed the dimmer, which I rewired the same as the original, but the problem remained. We have now replaced the ceiling rose & light fitting and tried various types of bulb, a hologen flickered rapidly and then went out, a low energy bulb flickered initially, went out and then came back on very dim; traditional bulbs only comes on very dim.