cannot delete corrupt backup of iPhone

I have an iPhone 4S. I've recently doubled my hard drives, by replacing my dvd player with the original hard drive, and installing a solid state hard drive where the original was. I have most of my applications on the original HDD.

I've had many problems, amongst which are.

1. iMessage doesn't appear to be working correctly, which I've traced to the fact that my contacts are missing.
2. I can't backup my iPhone via iTunes. I keep getting the message that I need to delete a corrupt backup. I've been to iTunes > Preferences > Devices. There are no backups there to delete. But it won't create a new backup.

Any clues?

Cheers - Suella