Erradic/epileptic mouse behavior - Help!

So, suddenly the mouse pointer is all over the screen.
Like an epileptic system operator is in charge. It stops
responding. Flying from side to side, pointing at stuff,
opening, closing things, left clicking and right
clicking. After about 20-30 seconds of this the mouse
arrow freezes and the mouse isn't responding. After a
reboot I sometimes regain control of the mouse, sometimes
it takes several reboots.

This has happened several times in the past. Then
suddenly stopped for a long period and now it's started
again. It normally happens within the first 4-5 min of
using the PC, a few times suddenly during a long session.

For a time I thought it was a heating problem so I've
installed new fans, removed the cabinet and so on,
however that didn't seem to cure it. Then I thought it
could be virus/spy-ware/worm thing so I ran all the usual
programs but that didn't cure it. I've changed mouse a
few times to test that as well both optic and normal.
Tried to update the driver for both the brand-name and
for the no-name mouse. Also un-pluged it and re-pluged it.

Only unnormal issue I have found is that if I unplud the
mouse after an incident and then reboot the PC, the
system fail to detect that no mouse is present and it
shows a mouse pointer at the center of the screen.
However only found this once, but thought I should
mention it.

(Running tests combined with a mouse that either doesn't
work or only work a few minutes is a patience testing
process).

I'm getting desperate. Anyone tried anything similar?

Help!

Søren