When i take a photo it looks bright, sharp and vibrant colours, but when it is transferred to my computer it looks so bad. Very dull and dark with weak colours. I have to brighten and increase contrast plus give it lots of colour saturation to get it close to the picture on the camera screen.
The LCD screen on the back of your camera Lies like a politician! They are designed to make every shot look as good as possible so when you look at them at the store you will say, "This camera takes really good pictures!"
Remember, typical DSLRs now have resolutions of around 20MP, give or take a few. The LCD screen on the back of most DSLRs is about 1MP, give or take a few. What this means is that blur that is less than about 5 pixels wide (or high) will be combined into a single pixel on the LCD preview screen and will appear to be sharp!
Preview images displayed on your camera's LCD screen are also sharpened and usually have a bit (or more) of contrast and saturation added to give them a little "punch". Hey, the camera manufacturers want that preview image to look incredible when you make a sample snapshot under the crappy light at the camera store!
Keep in mind that if you are saving raw files, you're not viewing raw data on your camera's LCD. What you are seeing is the jpeg preview image generated by the camera that is appended to the raw data in your raw file. When you open the raw file on your computer your viewing application probably isn't using the same settings to render the raw data into an 8-bit JPEG-like image on your computer's screen. For more about the different ways cameras and computers render the same raw data, please see: Why do RAW images look worse than JPEGs in editing programs?
I think this boils down to your computer's calibration.
It's very typical for computer screens to be set to brightness and contrast settings that are well of what is required for good photo display.
I'd suggest trying these tests to see what state your display is in (and how to adjust it).
I notice Michael Clark's comments about the LCDs on cameras, but I think that these LCDs have to have "boosted" settings simply so that they are clearly visible outside. I don't think they are deliberately adjusted to mislead people.
There could be several factors that would make a difference when viewing same image in your LCD screen vs on your monitor. Note that you never really lost any quality when you transfer the image to PC from camera. It's a digital file that is copied bit by bit.
Your LCD screen is tweaked by manufacturer to show the image as vibrant as possible. That's typical of most Samsung phone screens.
Your monitor might not be calibrated correctly in terms of color accuracy. You need to run the color calibration to ensure the color is correct.
It's also possible that some image files uses color profile stored within the file, while your PC program could not interpret the color profile correctly.