weird things keep happening

My nice new computer keeps doing strange things. It
happens most often (tho not exclusively) when I'm opening
or saving a file; suddenly the screen starts to flicker,
windows start opening and closing, the start menu shoots
up and then down and the arrow starts moving around in a
fashion that seems unrelated to the movements of the
mouse. If I control-alt-delete it usually settles down
again (tho nothing odd shows in the task tab of the task
list box). Our virus software is up to date and can find
nothing wrong. scandisk and defrag have, if anything, made
it worse.
What could be causing this and how do I stop it?
(might there be a connection to the non functioning help
and support which is going to be reinstalled when the IT
guy has a moment)