You can block a program in Windows using built-in tools like the Local Group Policy Editor, Registry Editor, or Windows Firewall. Below are step-by-step methods for each approach.

Method 1: Using Local Group Policy Editor (Windows Pro editions)

1. Open the Start menu, type gpedit.msc, and press Enter.

2. Go to User Configuration > Administrative Templates > System.

3. In the right panel, find Do not run specified Windows applications and right-click it.

4. Select Edit, check Enabled, then click Show.

5. Add the executable file names (e.g., appname.exe) you want to block.

6. Click OK, apply changes, and restart your PC.

Method 2: Using Registry Editor

1. Open the Start menu, type regedit, and press Enter.

2. Navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies.

3. Create a new key named Explorer under Policies.

4. Inside Explorer, create a new DWORD (32-bit) Value named DisallowRun and set its value to 1.

5. Create a new key named DisallowRun under Explorer.

6. Inside DisallowRun, create a new String Value named 1 and set its value to the program’s executable name (e.g., notepad.exe).

7. Repeat with 2, 3, etc., for more programs.

8. Close Registry Editor and restart your PC.