In my experience this behaviour is caused by either not having an external power supply, or by having one that functions badly. In most cases external disks, especially large ones, need their own power supply. Look into that. Or contact the retailer/manufacturer directly and report this.
As far as the disk corruption goes, that isn't surprising. You could try iRecover to copy files to safety, but only after having fixed the disconnection problem. Do not run chkdsk or any other "repair" software. People who offer that particular advice have no idea what they're talking about, and they seem to mainly hang out in the type of forum where you asked the question. Avoid. More info here: http://www.diydatarecovery.nl/FAQ_irecover.htm#F8