Is your PC a works PC/Laptop? If so you maybe under whats called GPO (Group Policy). This adds or removed features from users to prevent access and use. Companies use it to reduce errors and tighen security.
When in the control panel switch to classic view on the left side. Double click system and go to hardware then the advance tab. In the performace box click settings and you will see the Virtual memory selection in the advanced tab.
Worth noting that if you have another drive in your pc, change the page file over to that drive, it speeds things up a bit.