macmini sound I/O

Sound issiues

1) Rrecently added an isight camera (for skype) but no sound--Box checked to use isight under Preferences sound --but to no avail..\
Also tried an in-line mic--(using ext jack)--and nothing--What to try next??--Can I test jack? Software??

2) And tryed to add some USB small speakers (Altec) --and under Preferences it simply says to choose or add speakers but thye don't show up as an option--The speakers have an option to use the 3.5mm jack for input but that doesn;t give power to the speakers--do dn't work that way either?

Frustrated--deaf & dumb???!!