These could be popup's that disable the toolbar. You best defence might be
to install a Popup Blocker. Try the Google Toolbar. http://toolbar.google.com
I'd suspect that the blocker is not configured properly. Also a
possibility of adware installed on your computer. If you have not
installed an adware removal program (ie Lavasoft Ad-Ware 6.), I'd
suggest that as a next step.
