I have Seagate 2TB external hard drive. I am using this hard drive to backup my files (manually, not with Time machine). The main problem is that external hard drive doesn't work stable. The problem is that sometimes(very often nowadays) I cannot see this drive when I plug it to my Mac. Drive can be seen in disc utility but it can't be opened to copy files in it. I'm trying to verify and repair disc in disc utility but it also doesn't work. Do you have any suggestions guys to solve this problem?