To turn on click lock follow the below steps:
1. Click Start--> Click Control Panel.
2. Double Click The Mouse Icon.
3. The Mouse properties Windows appears with buttons, pointers, pointers options, hardware’s and track point tab. The Buttons tab is already selected by default.
4. In the button tab--> third and last option is ClickLock and below it you can see the check box with the label Turn on ClickLock.
5. Click on the check box to enable the ClickLock as mentioned below. Now you can see the settings button is enabled click on it to adjust how long you need to hold down a mouse or trackball button before your click is locked.
Click here: To Enable Clicklock In Windows 7