If the files open OK on the newly acquired PC I don't think they could be as much as a single byte different. Do a file size check just to be sure. Right-click on the filename in Windows Explorer for file properties and note the file size in bytes.
It seems more likely to be a difference to do with display, or number of colours. Right-click on desktop and check the settings for each of your systems, and tell us about the display on both systems. eg. 15" monitor 256 colours 800x600 pixels.