Jittering Cursor

Hi,

I am new to the forum. I did a search for jittering cursor but did not find and threads relevant to the problem unless I looked in the wrong place.
As I was working this morning, my cursor slowly began to wander just a bit. I thought it might have been dirty and cleaned it (optical mouse). It accelerated and now jitters quickly in the area that it should be - ie: it doesn't wander around the screen, just jitters around near where it should be. It will do this even after rebooting or even with the usb mouse unplugged. I have run a scan with my antivirus and turn up nothing.
Is there something I am missing or does anyone have any suggestions as to what I should try?
Thanks in advance.

Are sometimes the last to be found. It was just something stupid on my part.
In cleaning and blowing dust out of the computer yesterday, I mistakenly plugged two mouses back into the pc without realizing it.....

Thanks for the help anyway.