External hard drive had lost files

I've got this 1.5TB Toshiba external hard drive and I already have files there amounting to almost 500GB. Then this morning, I copied files from my friends laptop. When I accessed my external hard drive in my laptop after copying those files, the older files w/c amounts to almost 500GB all got lost, and what is left are the files that I had just copied earlier. The memory usage had lost the 500GB used space and it now has only a used space of 133GB, the size of the new files that I copied earlier. The hard drive tells me that I had deleted the older files but I really didn't. The external hard drive's icon also got a shortcut and when I click on the shortcut, it will lead me to a folder where there is the external hard drives icon. When I click on this icon, it is where I can find those new files but my older files aren't there anymore. I can surely say that the files are not hidden because it doesn't eat up any memory anymore. Can someone please help me. I really want to recover those files.