It depends how you want to go about it.
Data Saving Method
Remove hdd,put into another computer,run data recovery software such as ZAR X or Recuva
After Recovering data,format and install back into the thinkpad
Get a windows iso.Go to windows website if you dont have and download,then transfer to thumbdrive or Disc
Using your thinkpad,run the iso and install windows normally.
Fresh start without data.
Do about without recovering data