There is usualy some buttons on the screen, click on them and try to find out how to change contrast. It is different on different screens so I can't help you any more.
Yup, there should be like a few buttons on your computer-screen.. there u can change the contrast etc
Is it a flat screen LCD? If it's a MONITOR MONITOR..you know.. the big boxes with light and messed up buttons.. I say trash it.