My laptop's getting slow so I want to format. But I can't seem to backup my data on my external hard drive. This 500GB drive already contains the backup of my other laptop, but it has just about enough space to contain the backup of this one, too. It has 283GB free and my computer has only 277.5GB stored data.
I tried backing up my data to it using Windows Backup & Restore, but around halfway through it says that a backup file could not be created because of an I/O device error (the error code is 0x8078002A). I've done this several times with the same results. I ran a Chkdsk on my hard drive as admin, but in normal mode. Windows found no problems.
How can I fix this?