Reinstalling Endnote

I want to format my PC and reinstall the programmes/software. 

Will this cause problems with my Endnote license?

Not if you have the activation code written down somewhere (a muliparted number with dashes).

The Single User License entitles you to install EndNote on up to 3 computers for personal use at one time. If you re-format your computer and re-install the software, you are covered within the licensing agreement.