I am trying to apply for AP MBBS but the link to register is not working in any of the browsers.

Dear Prakhya, the link https://apmedadm.ntruhs.ap.gov.in/
is correct. However as today is a weekend and too many candidates might be trying to register, you might be finding it difficult to register. Infact, the server is slow. So we would suggest you to wait until late night or register early morning when the traffic to this website is comparitively less.