OS x 10.9.5 display has mind of its own

[faunika]

Hi. I inherited an old mac book last year. From the beginning the display would act up. Getting larger - super large then small - back and forth rather quickly. Some days i can hardly use it. So theres that. Then last night i was editing pictures using preview, working out of a folder on the desk-top within a finder page. When i was done resizing them and changing the file extensions, specifically by taking a screenshot of a picture with a .png extension so i could turn it into a .jpeg, i then deleted the original. Im sorry that was such an awkward sentence. i did this for about 4 hours and the first hour the was a definite lag that grew into an issue. it was obvious that it was overloaded and stuck on trying to delete a bunch of files. i tried to find it so i could make it stop. Windows has something for that - i couldnt find anything. so the problem involved finder and preview and desk top - and frequently it would say something about "YOUTUBE. And tonight it is dropping letters. i have enclosed 2 reports that