All my videos have gone?!

Ok so this is the issue.....Last week I opened my 5th gen iPod touch on my mac at work, I seemed to have loads of space and when I checked it had deleted all my videos and music. So I just wiped it and restored it.

I then loaded the music and videos again and it seemed fine.

So yesterday I added some videos to it on my mac at home and watched a few, then was watching one in the taxi this morning. I go to work, added a few videos and although it shows all my videos, about 30 of them and all my music when I click on them it comes up with ⚠ and they aren't actually on. So it's deleted them again!

Now I have it set to manually managed music and videos so what's the problem?

I don't mind putting stuff back on but I don't wan this to be a regular occurence.

Any ideas? Thanks loads in advance,

Dave