I have had a look through the Umbraco forum and not mananged to find a solution to this problem that works in my case.
This has happened once before and I had to restore the site from a backup but several weeks on the same thing has happened.
All other parts of the site are fine, there is content in the Media sections, the Temapltes are still there and everything seems to be as it should be. However the Content section is empty and just has the bin.
I have reloded nodes to no avail.
Checked folder permissions, again everthing looks to be ok.
Checked for AjaxControlToolkit, there is no DLL file for that module so can't be that.
Something must be causing this to happen but I don't know what. Haven't even logged into the backend for a while.
The site is still working fine and everthing is as it should be, just the backend that is having issues.
Any suggestions as I don't want to have to restore the backup again.