If you just bought it, get your money back and try a different brand. This happen to me a couple time; now I know what brand not to get. But off hand...I forgot, hehe. What brand do you have?
If I unplug it everything will run smoothly but it is plugged in things will slow down. Windows doesn't recognize it, I can't run chkdsk on it. It says Check Disk Utility has encountered a problem. Also says I/O Device Error. I rebooted my pc with it plugged in it went to the screen right before the mouse arrow shows up and stopped. Then I unplugged it and my pc started up. Tried to change the drive letter, and error check but nothing happens it just freezes my computer until I unplug it. I also tried to defrag it showed up in the list of drives but if I clicked it everything would freeze again. Same thing would happen when I click it on the My Computer folder. What should I do? I'm gonna reformat it next if no one has a better idea. Thanks.