Passport Essential won't back up

I’ve a 0.5TB Passport Essential running on an XP Pro SP3 system.  It was working fine but in the last week or so won’t back up my data as it used to.  If I click the back up tab it catagorises data and shows how much is ready to be backed up (but no yellow/orange bands on the different types of data).  If I click the ‘Run Backup’ button, nothing happens and the ‘data backed up’ numbers stay at zero.  I’m concerned as I want to securely back up my digital photos and they are not there on the Passport.  I’ve checked by clicking ‘Retrieve’ and seeing what’s there.

I’ve check to see if I have the latest firmware and software.  I needed a firmware update but this has not got rid of the problem.

Any ideas please?

tengo problemas al querer copiar de una computadora que tiene windos xp