Do I format malfunctioning EXTHardDrive

Hello,

I have a 750GB Medion Est hard Drive with lots of my small business's photos on it.

I can look at the folders on Windows Explorer to a point and then after going a certain depth it asks me if I want to reformat the disk.

Can't open any of the actual pic or video files that I can get to.

Should I format it to regain access to the files or will this (as was my first thought) just wipe everything?

I could really do with not losing these files so all help would be greatly appreciated.

NB I am working on Vista or XP depending on which pc I use and the drive is connected by USB however it does have a SATA port.

Thanks


Emma