I am doing some reserch on HDDs. If I am unable to back up files what causes this? And I need to know why I am unable to access files on HDD.

Hi lito, welcome to the PCHF!

The main cause of not being able to access hard drives is File Allocation T able (FAT) corruption.

Try plugging it into another computer and see ifyou can get the files off, format it and put the files back on.

maybe i will be able to help you if you do spec a little more about your problem,

i had a very similar case not long ago, i screwed up the partition table, so i did restore it with an msdos based app. there are lot of them in the market, you will need to create the boot disk from another pc. but try that. i cant remember the name of the app i used. look over the internet for partition recover.