I've had these couple of problems for the past few weeks.
I thought my high CPU usage was due to the NextGen gallery. It was actually due to the WP-UsersOnline plugin. Deleting/Deactivating WP-UserOnline, thus lowering my CPU usage, got my slideshow widget working.
[To find this I deactivated all plugins and re-activated them according to importance, starting with NextGen. I was monitoring my CPU usage with each plugin I re-activated to find out which one was usingg all of my resources.]