I was in a similar boat and through a series of circumstances had to get an S8+. As long as you keep your expectations reasonable, it's a great phone. There are better deals/options available, but in a time crunch it's not a bad option to go with.
General process would be to use a different cable, try a different port, if using USB 2, try USB 2 and vice versa, Remove drivers completely, reboot system, reinstall fresh. Reboot phone and try it all again
I remember back in the olden times i sold a hard drive to a guy on Ebay. I ended up getting hosed by the buyer. There was no doubt that was his intention. Paypal/Ebay screwed me of course. Never again.
They've always done this, I'm not sure why this point in particular would suddenly make people lose confidence. Plenty of other reasons to choose from.
I've used Virtual Desktop to watch qutie a few movies and had a good experience. It helps to have a higher res movie file of course, otherwise it's terrible.