I bought a new smartphone and everything was fine when I connected with my computer. I don't know what exactly I did but after I unplug it an app called 'System UI' was spamming my screen to turn off USB Storage but the button was inactive. I didn't know what to do and I forced stopped the app. Now some features are temporarily inactive from this charging all my photos are missing, my apps that I had installed now are uninstalled. Please tell me HOW TO FIX IT ?
Did you already try rebooting the phone to force a remount of the storage devices? If not remounted you should be able to mount it manually from Settings > Storage.
Certainly reboot. It sounds like you might have unplugged it while the computer was still accessing the usb storage. Make sure to use the safe removal feature and try again.