My phone has been dropped and one-fourth of the screen is black.

My phone has been dropped and about one-fourth of the screen is black. Apparently, it can be touched there and it still works. Aside from the partial black screen, there are few thin colored lines that appear sometimes and that they run across the phone also. This problem existed since a month ago. The display is the only problem here. This problem is quite annoying since I can’t see a portion of the phone clearly. The pictures below show the phone in question (The pictures might be a little too many to provide, but oh well):

Please help me to fix this problem…