Thanks for your help, the drive is external hard disk with a usb connection.Yes it shows in computer and I can see the properties. I changed the owner with full access,but it didn't help. I connected the drive to an XP machine and it works fine and I can access my files.
I tried connecting it to another Windows 7 macine and it didn't work and gave me the message access denied,although i had no problem accessing my files with the same Windows 7 machine six months ago. Could it be some Windows 7 updates.