Temporary Internet Files act as a  ‘cache’ to speed up page delivery. Deleting temporary internet files to save hard disk space is generally okay.  Read more details here.

Power, wifi, and other icons are offen missing from the taskbar after a Windows update.  In most cases, logging off and on again will solve the problem.  If the problem persist, consult the following pages:

http://www.mydigitallife.info/fix-network-clock-volume-and-power-battery-system-icons-missing-with-disabled-or-grayed-out-check-box-options/

http://www.winhelponline.com/blog/notification-area-icons-missing-in-vista/