Windows 7 "resolution quality issue"

i got a new custom build PC from a shop to my little brother yesterday and the guy who sold it to me told me that the PC has an original version of windows 7 installed on it.
after me and my brother turned on the PC and installed some of programs and games on it , we noticed that windows 7 image quality is not that good..
the task-bar and the start menu icon and text sharpness and the backgroundsand the prepering to lunch image that shows before windows explorer show are not as sharp and crisp as it should compared to my laptop and my PC ..

so after i got back to the guy that i got the PC from he told me he is sorry and and the win 7 version was "pirated" not original, and give me a windows 7 product key.
so after i activated my version of windows 7 and become a legit , the problem of the resolution quality didn't solve . . even when we play games on it . . the image quality is not sharp and crisp as it looks at my PC

i checked the Nvidia control panel and checked that the resolution is set to 1080p and from the control panel it show as 1080p and the monitor he use is the same as my monitor "samsung syncmaster B2330"

so it thought that since its was a pirated copy from a site like torrent . . the person who uploaded it has done some modifications to reduce the size of the package . .
and he may deleted some windows 7 resolutions files or icons files that responsible . . etc

because when i changed the resolution to 1600x900 from the control panel on windows 7 and also change the resolution from the monitor . . the image looks as it should !

so can some one help me by telling me what files should i update or replace with others to fix the problem . .or just help me by suggest me a solution . . thanks.

by brother PC:
AMD phenom ii x4 , gtx 560 non ti, 880 asus board AM3 , samsung syncmaster b2330 1080p , windows 7 activated