You will not be able to download the full version, only the trial version which cannot be activated.
When downloading a program, you should ALWAYS make a copy and store on an external drive or DVD for later re-installation purposes.
All you can do is to contact Technical Support, you will need to provide proof of purchase, explain that you have installed a new operating system and they may provide a new download link.
Robert
Intel i7 930, 16GB ram, Radeon HD 5770 1Gb,Ver. 14.12 Win7 64 bit
Intel i7 7700 HQ, 16 GB ram Nvidia GTX 1050Ti 4GB dual drives 1 TB SSD + 1 TB HDD Win 10
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