Sorry you’re having trouble. :-/ GIF and TIF won’t work. You can use either SVG, PDF, PNG or JPG. (99% of my files are a combo of SVG and PNG as they seem to be the easiest to deal with.)
It’s so hard to do these things without seeing it, so sorry if this is seems like I’m pointing out the obvious. From the Home>upload>select file>double click. Ignore the “drag anywhere” dialog if it pops up. As the image starts to load you should get the “Hang On…” dialog box and then the “rendering” dialog. To test it out and get use to it, I’d try a few different SVG or PNG file first.
If it forever hangs on the “drag anywhere” box, it might be a wifi issues, but I’m not much help with that. I did just try and upload images to make sure there wasn’t some weird issue effecting us all and they worked fine on my end.
If you haven’t seen this yet, the matrix is the best resourse for getting to know your GF.