Right click on the shortcut icon and set it to run in Win 98 Compatibility mode. Some of the older AMD dual-core (and a very few older Intel dual-core) processors had issues for whatever reason. By running it in compatibility mode, it forces the processor to use only one core which is a 'stop-gap' for this issue.
If this does correct it, check to see if there are drivers or updates available to correct this issue so that you can once again enable both cores.