Right-Click your desktop, go to Arrange Icons By, then check "Show Desktop" to get the icons back. Mouse over to the edges of the screen to see if the task bar shows up. If it does, then right click it -> Properties, uncheck AutoHide. If it doesn't pop up, then Ctrl-Alt-Del and see if explorer.exe is in your process list. If isn't, then go to File -> New Task in the Task Manager, and type explorer and hit enter. Now it will either open an explorer window (to browse files), or start up the taskbar and stuff again. Either way, go to C:\Windows\ and open system.ini. Then, IF IT ALREADY EXISTS, make sure the Shell line does not have a semicolon before it and reads something like explorer.exe (my comp doesn't have the shell line for some reason). Dont add it if it isn't there (who knows what could happen...
If the New Task thing fixed explorer, then Create a shortcut to exploer.exe (the one in C:\Windows\) and put it in the start-up folder ofr all users (C:\documents and settings\all users\programs startup I think). Someone will hopefully tell you the real way to do it.