Fiona,
I have an Inspiron 1420, and a couple of days ago, I started having
exactly that problem. I usually either use the power button, or a bit
of software which I can access from the desktop. Both have been fine
until now. As you mentioned, forcing a power off with the switch has
many undesirable consequences.
As an experiment, I used the Start | Turn of Computer route, and
walked off for a few minutes. When I returned, the computer was off.
Since then, I have been using the same method, and it is behaving
normally. Some other anomalous behavior has also stopped. Apparently,
getting a clean shut down cleared something up. Of course, it might
just be a coincidence that it worked this time, but easy enough to
try. If it continues to work, I will try something wild and crazy
like the power button again.
--
Alan