Thank you for asking here! For your question, after reformatting your PC's hard drive, and then reinstall Maximum Security the same PC will count as another machine. But don't worry, you can use your Trend Micro Account to check/add/remove devices covered by your Maximum Security. You will be able to see all the PCs that has Maximum Security installed and manage which PCs you want to enable/disable protection Maximum Security using the following steps: Deleting previous Trend Micro installations in your Trend Micro Account (MyAccount)
Please let us know if your question is answered. Thank you!