Mac Mail: Can't attach any files

Hi,

If I am in the Mac Mail composer window and press the paperclip, it gives me a dialog to choose a file, which I do, then the dialog disappears and there is no attachment (have tried sending, no attachment at the other end).

If from Finder, I share a file via email, it starts an email, shows the file as an icon BUT the file is zero bytes ??

Similarly, if I drag a file from finder to an email composer window, it appears as an icon but is zero bytes.

It does not seem to matter what type of file (I've tried many -> zips, txt, .docs etc., etc.).

I have only had this computer for a month so am not sure if this has ever worked (my wife tried telling me it wouldn't attach files but I assumed she was doing something wrong).

It also doesn't matter which user I use and I have tried fixing the file permissions with the disk utility.

Any other ideas ??