Access to external hard drive

[PC45]

For some months we've not been able to access our Maxtor 500gb external hard drive, nor to back up files to it. We run Windows 7 on our PC. We get the system message that the relevant drive or network connection is not recognised. What can we do, please?

 

[popatim]

Whats the model# of the Maxtor?

 

[PC45]

It's a Maxtor Basics Desktop Storage. Model no: PN 9NZ2A4 - 500.
There's a SN number too: 2HBA9CZB.