Solved External Backup shows 70GB free of 465GB total

On 'Computer' from the START menu it shows 'K' drive (external 500GB Buffalo 6 yrs old) as having 70GB free of 465GB total.
However, when you click on this drive it shows the old backup as empty when formerly (last year) it was almost full.
However, the new backup shows only 4.58GB used.
The software is Memeo which is a separate issue though and it stopped working about a year ago (worked ok for 5 years) and Memeo downloaded a newer version for me in the middle of last year. It originally came with the Buffalo Ext. HDD.
But how can the 'K' disc show 395GB used of 465GB but the details of the 'K' drive seem to only have 4.58GB on it?
Something must be wrong.
Also, when I set up the new backup plan using the new software there was only enough room on 'K' drive to have Documents, Music and Pictures backed up because the size of the Videos prevented me adding that as well. I intended at a later date to remove the videos from the old backup plan and create a new backup plan for them. Now I can't find the backed up videos at all. Many of the backed up photos will not open either. What a mess!
But I first have to sort out what is going on with this discrepancy with 'K' drive.
Thanks,
Phil.

Update. I contacted Buffalo who said to send them off the disc but I decided to ring them and they said that my disc was out of warranty. I had two direct link sessions with Memeo and they could not fix the problem. On the second session every time access to K was attempted a window would pop up saying if I wanted to access K disc then I would have to format the disc. Each time the Memeo guy said not to format the disc. After the session was over I formatted the disc which wiped it clean including any old backup plans except for the last one. I then made a new backup plan and removed the old remaining backup plan. I let the computer run all night and backed up all my Documents, Photos and videos from D to K. Problem solved!