Explorer no function - no taskbar, no menubar, no desktop icon,etc

i company faced the problem recently. Some of the computer with the problem

after the computer start. user can login their account but explorer no

function. safe mode also same. then i try run explorer.exe under new task in

the task manager. but it came out a error.

but finally i got the solution from other forum. i make some changed in the

registry then the problem solved. i delete the following registry. the

registry is not available in my other computer.

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Image File

Execution Option\explorer

everything solve after i restart the computer. but i wan to know what is the

real problem? why the registry changed?

Guy, any idea? is it a virus or ......?