Hi. Icons may disappear if you don't have an admin account and some programs have been installed for a single user (and not for all users).
As this is an Antivirus forum, if you consider it could be a virus related issue, the first suggestion would be to... scan your computer :)
You may also want to use Spybot and Ad-Aware Personal Edition from Lavasoft. They are both free and very usefull.
Let me know how it goes.