Assuming you're not on a corporate network that the admins have disabled
such tools.
Try ...
Start
Run
type
gpedit.msc
<Group Policy opens>
navigate to
User Configuration
Administrative Templates
System
in the right hand side there's an option
Disable registry editing tools
default setting is Not Configured
Quote the explaination from that option:
"Disables the Windows registry editors, Regedt32.exe and Regedit.exe.
If this policy is enabled and the user tries to start a registry editor,
a message appears explaining that a policy prevents the action.
To prevent users from using other administrative tools, use the "Run
only allowed Windows applications" policy."
--
Steve Parry BA (Hons) MCP MVP