Cant get any sound when plugging guitar into input from amp!?

i want to play my electric guitar through my pc so that i
can play to my friends and record stuff using software. i
know it wont work by directly plugging the guitar into
the input (have also tried this) so i plug the guitar
into the amp, then get a cbale and plug one end into the
headphone socket in the amp and the other end into the
sound input in the PC (so that it will get exactly the
same sound as the amp would give out as its coming from
the headphone socket but nothing comes out of the pc. i
have tried to adjust the sound settings but im not an
expert on that part. my friends have done this but ii
just cant seem to get it to work!

so has anyone got any ideas or any information on
downloads i need?

thank you very much