system error

When I try to load software or even when I click on the start menu for my dell express service code I get the following error message-
The Win16 Subsystem was unable to enter Protected Mode, DOSX.EXE must be in your AUTOEXEC.NT and present in your PATH. The problem is that DOSX.EXE IS in my autoexec.nt and present in my PATH. No one at Dell or on the microsoft website has been able to help me with this problem.