i NEED HELP TO DOWNLOAD, INSTALL AND ACTIVATE MY SOFTWARE IN MY NEW (ONLY) COMPUTER.

There's absolutely no need to shout.

Using lowercase letters, your message can be read easier, and it 'sounds' friendlier.

(Or did your Caps Lock key get stuck?)

Anyway, you'll have to be a bit more specific on your problem.

- State what you are trying to achieve.

- What 'software' do you want to get on your compute?

- What do you have, and what do you miss?

Maybe the following will get you on the way:

https://community.ptc.com/t5/Mathcad-Installation/How-to-Download-Mathcad-Prime-11-0/td-p/1034739 

https://community.ptc.com/t5/Mathcad-Installation/Step-by-step-Installation-Instructions-for-Mathcad-Prime-11-0/td-p/1034740 

and in case of other problems:

https://community.ptc.com/t5/Mathcad-Installation/All-About-Mathcad-Software-Installation/td-p/706433 

Success!
Luc