You probably have a virus that makes them all hidden, unless you mean the whole bar is missing.
If it's missing, hit the Start keyboard key to bring up the menu, and in the Run field type in C:, hit enter. Browse to Documents and Settings, All Users, right-click on the Desktop folder, uncheck the Hidden box, Apply. Right click on the Start Menu, do the same. Then go though the virus removal guide in the root of the forms here.
OMG Thank Youuuu Ssoooo Much!!!! I Was SO Stressed after I tried just getting the 'volume' icon back, I read something on another site that some one said to do, then BANG - ALL of my home screen icons, the bar, and start button dissapeared! Then I found this and its worked so thank u , thank u , THANK YOU !!!!
(what about your volume icon, did U got it back too or not?
If U can't see it in your taskbar, just go to control panel>Sound and audio devices >Volume tab>and check Place volume icon in the taskbar.
If U still can't see the icon it may be hidden or U may have a sound driver issue)