Desktop not displaying

Hello,

I have encountered the following situation on a brand new
PC a couple times in the past 2 weeks:

I boot up my computer and after the Welcome splash screen
when the desktop should display, there is no desktop. The
background colour displays, and I can CTRL-ALT-DEL to
task manager. After the set time, the screen saver will
initiate as set. However I see no desktop items, no Start
button or task bar.

I reboot the machine with the same result. Switch the
machine off and start again...same result.

I have had to reformat and install win XP twice. No
problem as this is a new PC and as yet does not contain
much data. However, I fear that after an extended period
of time this will cause trouble.

Is this a known issue and is there a work around?

Thanks.