I have 500 gig usb drive and all info vanished.When I plug in in it appears to be totally unformatted.

That sounds abnormal but here is how to see. Plug the disk into computer and make sure that it registers. In windows right click on my computer or computer in windows 7 and select manage then select disk management. This will show you the hard drive and it partitions. You will be able to see the partitioned drive here make sure that it is occupying the whole disk. If not format the disk by right clicking the drive and selecting format i would go with ntfs file system. It is not uncommon for the disk to be smaller but not 50 gig. if the format doesn't fix it take it back.

i think there is some virus with your hard drive and that vanished all the data. u try to put some anti virus software to your comp..or u can seek the help of this site

Under DISK MANAGEMENT, you should see the 500GB drive.
Does it show as "formatted" (FAT32? NTFS?) or as "unformatted" ?
If "unformatted", then right-mouse-click on the drive, and 'format' it, and assign it a drive-letter.

Check your jumper settings on the drive. Make sure you 80 gig hard is slave if you want your 500 as master.

You better check with the Seagate people. This seems to be a problem with the casing. And since you're under warranty, you can get a replacement.

install usb 2.0 drivers again

try replacing the USB data cable

load the driver for mac use, the external hard drive comes with cd, the mac driver should be inside, load it to your mac computer. if you donot have the cd go online to western digital and download it. just load the driver and u will be fine, make sure u connect the cable in right places.

I’m happy to help further over the phone at https://www.6ya.com/expert/mustafa_06f84c65ab5cc745

I am having the same problem!!!! I have my time machine backups on there and I cannot access them! Class action lawsuit???

Your computer must have a firewire connection.