Don't know whether the free version will accept a license key, but definitely archive your licensed version installation files, for reinstall if required.
What are the specs for your PC - CPU, GPU, memory, avail space on the drives, etc.? Knowing that may help others to help you.
Check the chip manufacturer's WEB site for an updated video driver...
http://geforce.com/drivers (NVidia)
http://support.amd.com/en-us/download
http://www.intel.com...detect/graphics
If problems arise, roll back via Control Panel|DEVICE MANAGER|VIDEO ADAPTERS|<your video adapter|DISPLAY tab.
Any error messages being displayed? When it finally does respond does it work as it should?
Have you cleared Windows temp files lately? Open File Explorer/Manager, right-click the C: drive and click on DISK CLEANUP.
Have you defragmented the hard disk (do not defrag an SSD)? Control Panel|ADMINISTRATIVE TOOLS|DEFRAGMENT AND OPTIMIZE DRIVES.
If all else fails... http://www.nch.com.au/general/contact.html