Data Execution Protection is invincible

The DEP on my system just wouldn't let me turn it off. When OneCare informed
me that it has blocked a program from accessing the internet, DEP closed down
OneCare so that I cannot opt to allow the program. When I go to Help centre
to seek guidance, DEP shuts down Help & Support. I then went to System to
change its setting, it shuts down Advanced System Settings before I can do
anything.

helppppppppppppppp

 

I have virtually identical problems but in my case DEP keeps blocking
"Windows Event Notifications Service." For some reason this results in
making the Windows Vista interface look very much like a Windows 98 interface
(for example: most of the menus have that old grey color, tacky 3-D look, the
buttons have become blocky, and even the task bar reverts to the old
rectangular grey one with the rectangular start button.) To my knowledge, I
don't have that OS installed on this computer. This has been going on for
months and I've finally become fed up with it because it happens very
randomly. Can you please tell me why this is happening?