i can't scroll through photos uploaded on a sd card

With the amount of information you've provided it's impossible to offer a solution. We can't see your computer so we need to know the details of your problem and setup, i.e.:

• uploaded to where and how uploaded?
• what are you using to try to scroll thru the photos?
• what system version are you running?
• when were you last able to do what you want?
• what type of Mac?
• what fixes have you tried?
• did you apply any updates or upgrades just prior to the problem occurring?

Do you see the SD card on the Destkop when you insert it into the card reader slot? If so open it, open the folder containing the image files, click once on of of the files and hit the Space bar. you should be able to view the photo with Quicklook and scroll between the photos using the arrow keys on the keyboard.

If you don't see the memory card on the Desktop check the Finder's preferences to make sure all devices are select to be shown on the Desktop: