Have you upgraded your GPU yet, or are you still dealing with the old one failing at startup periodically? Maybe it's a power cable issue (loose, etc.).
Also, with regard to image size, I just use MSPaint in Windows to resize an image to perhaps 45% for landscape images and that works for one that can upload to the forum. I go a bit smaller (35%) for portrait images.
As Albert Einstein said, "I could have done so much more with a Big Al's Computer!".