While i switch on the camera it shows a good display but after having one and two snaps the screen become dim and later on just the lining appears

Could be a problem with the LCD screen viewer or CCD sensor go to bad. This condition is the same when your pics are showed in the pc ? Are you check ISO settigns? If yes, and the problem continue, first... could be a problem with the LCD viewer screen, or, second choice could be a problem with the CCD sensor or go to bad; in both cases this isn't a job that you could solve yourself; this wrong include distorted images or abnormal colors, scratchy purple lines, blank or black pictures, and/or black videos with good sound being recorded on the camera's flash card.

I suggest check THIS LINK for additional details in this previous solutions for an Defective CCD (Charge Coupled Device) and next contact your Canon service. I strongly suggest (taking into consideration the age of your camera) to evaluate the cost of repair versus the cost of a new camera with similar features, before making a final desicion.

If your camera have some "anti-vibration" setup, check if this is activated, or its possible that this system is go to bad or need to be recalibrated.

Hope this helps.