Most likely, you are running out of system resources.
Are you running IE6 on a Windows 98 system?
If so, see if there is a newer driver available for your video card.
If the driver for your video card does not support DirectX 9, you can have problems with IE 6 on a W98 system.
It might also be worth it to scan your system for spy-ware.
Try AdAware from www.lavasoft.de
Finally, if you are running Windows 95 or 98, how long since Windows was last installed on your PC?
Windows 95, 98 and Me all have a "working" life of around 2 years before the system files grow so large that they can cause system crashes.
If your system has been up and running for over 2 years, it would be worth it to:
Back up your files.
Run Belarc Advisor and create a system profile:
www.belarc.com
Download the latest drivers for all of your hardware.
Format your hard drive, and install Windows clean and fresh.
As a side benefit, it can be amazing how much faster Windows runs just after a clean installation.
Chas