> The whole problem of OP is than can't run cpan

If OP can't run cpan, cpan is not installed

> CPAN is installed

Them the first line is false AND/OR the second line must be improved:

If OP can't run cpan, cpan is not installed _or_ is broken

...and the solution for this in both cases is to reinstall, as I say previously

If cpan is correctly installed OP _CAN_ run cpan, so please, could explain why do you say the opposite?. Maybe you are trying to say that you think the cpan is broken? why do you think this?

This leads us to the starting point. The whole problem of OP is most probably that OP is not using correctly CPAN. the right use is:

cpan> install Some::Module