It might not be a virus.

I'm assuming it's a windows machine.

Do a control alt delete, and fire up the task manager. See what your system usage is. Go into Processes, and click on the CPU column to sort by that. You may need to click it twice to get it to sort from highest usage to lowest.

Let us know what the top few entries are. Ignore the one that says System Idle Processes (but not the one that is just System if it's up there).

Try that with and without IE running to see if it makes a difference.

If you are running antivirus, ad-aware, or something like that, disable it and see if it makes a difference.