Enabling access to install programs through the registry can be accomplished in different ways. The correct method for your system will depend on determining what is prohibiting program installations. Common reasons include a disabled Microsoft Windows Installer (MSI), Group Policy restrictions or program's invalid digital signatures. Enabling access for any of these will require modifications to the Registry Editor utility. Proceed with caution when working with this utility. Errors in manipulation of registry keys could result in damage to your system's functionality.
Log into the system with an administrator account. Launch the Registry Editor. Click the "Start" menu, type "regedit" in the "Start Search" text field and press "Enter." This applies to Windows Vista or Windows 7. Click "Start" and "Run," type "regedit" in the "Run" dialogue box and press "OK," if using Windows XP, 2003, 2000, 98 or ME.
Expand the "HKEY_CURRENT_USERS" hive, located on the tree-directory on the left pane. Continue expanding the following keys: "Software" > "Microsoft" > "Internet Explorer" > "Download."
Right-click the "RunInvalidSignatures" DWORD value on the right pane. Choose "Modify" from the pop-up menu. An "Edit DWORD Value" dialogue box opens up.
Note: if "RunInvalidSignatures" does not exists, you need to create it by right-clicking the "Download" key (folder) on the left pane, choosing "New" and "DWORD Value" and naming it "RunInvalidSignatures." The value will display on the right pane.
Enter the number "1" in the "Value data" text field and click "OK." Close the Registry Editor utility.
Log into the system as an administrator. Launch the Registry Editor by clicking "Start" and "Run," typing "regedit" and pressing "Enter."
Expand the following hive and sub-keys: HKEY_LOCAL_MACHINE > Software > Policies > Microsoft > Windows > Installer. A "DisableMSI" value will display on the right pane.
Right-click "DisableMSI" and choose "Modify" from the pop-up menu. Enter the number "0" in the "Value data" text field and click "OK." This enables Windows Installer for all applications.
Close the Registry Editor.
Launch the Registry Editor as explained in previous sections.
Expand HKEY_LOCAL_MACHINE > Software > Microsoft > Non-Driver Signing.
Double-click "Policy" on the right pane. An "Edit Binary Value" dialogue box opens up.
Delete the current value, type the number "0" and click "OK." Close the Registry Editor.