If it is a low down hardware issue, the screen shot will not show it.
What kind of monitor do you have? The problem can be present on some older analog monitors.
Check you cable. A loose cable can do it.
Too make a screen shot, start paint or similar photo or drawing program. Either minimize or move the program to a corner, hit the nPrnt Scn (print screen) and then enlarge paint, select edit then paste. Save as a GIF or JPG file and attach it to your net post
The attachment is visible only after you post.