Answer to "Replaced D-Pad, But now top screen is backlight with no image."It sounds like when you put it together you may have forgotten to connect one of the ribbon cable strips for the top screen it happens to us sometimes too! Not to worry it just needs to be reconnected if it doesnt let us know we will be glad to help you any way we can!
Answer to "How much is are screen"It really depends on which vendor you buy it from. To get one in good shape and at a decent price I usually recommend ebay because they range from $25-$40. I hope this helps if not let us know!
Answer to "Why can't my Wii console read the disc?"If cleaning the lens doesn't work then you may have to replace the drive. But try either A. using compressed air as @jcarm75 said, or B. use a cotton swap and clean it. If all else fails then as a last resort just replace the drive. Hope this helps if not let us know and we can help!
Answer to "Console makes start up sound, but does not turn on."Its got to do with something eternally, having it being in a garage for a long time it could of damaged a number of things in the system mainly the motherboard because some garages are not climate controlled. I would say the best bet is for someone to look at it reason being its going to be hard to determine what it is unless its looked at and tested in a number of ways.