If your TV only has one LED that flashes different colours, it sounds like it might be a Sagem HTD501, not a HD D50. How long is it since the bulb was replaced?
If you remove the lamp assembly, look at the right hand side of the hole where the assembly was, there should be a hole about 20mm wide. Inside there you should be able to see some coloured glass, this is your colour wheel. Does it appear to be intact?
Does the bulb come on at all during the startup? If you have the front plastic panel removed, you can see if any light comes out of the base of the light engine.
Let us have a bit more in depth info, and I'll give it a shot at diagnosing the problem.