You should read http://www.sitepoint.com/forums/showthread.php?816011-PHP-vs-ASP-NET as this has already been discussed and I feel you will gain some pretty good knowledge from re-reading what others have discussed.
Sorry, but this is far too vague a question, and as you can see from the answer you’ve received, a simple search would have sufficed to answer the question. Please search (both the forums and via your favorite search engine), and if you’ve still got SPECIFIC questions, please feel free to repost.
In the meantime, THREAD CLOSED.