desktop randomly resets back to log-in screen
 

Strange one this, firstly the system:-

Hardy Heron on a computer with an ATI Radeon 9600 gfx card.

Sometimes when I log in the panels at the top and bottom of the desktop, rather than appearing first before the icons fill in, will kind of 'creep on' last from the edge of the screen inwards. When this has happened I can gaurantee that the desktop will at some point in the near future reset back to the log-in screen and will keep doing it until I do a reboot and get the normal boot into the desktop.

Infuriating!

Please help.

Look at the log files.