Look for the "input" button on your remote control. If you can't find it on your cable remote, look on the remote that came with your television. Use that button to find the USB. When you see the screen, your options will pop up.
On my remote, the "input" button is at the top. If this didn't fix the problem, post again and I'll try to troubleshoot your issue. I display pictures on the television screen quite often for dinners, church, and other events.