There are a lot of things that can affect a VOIP connection, not least the quality and speed of your internet connection.
Have you used VOIP (Skype) on this connection previously?
If you have details please post the connection details.
You might also do a speedtest on line which will give some detailed results.
Please post the results from this or another site ...... http://www.speedtest.net/
Separately you need to know if your MIC is working.
What type of MIC is it?
How is it connected to the PC?
Does it work in any other application?
Does it show on in the PulseAudio Control tab when in use
Do you see an indication of the MIC in use? (a varying horizontal line with MIC input)
Have you tried altering the MIC volume ..... up and down?
Is Skype set to adjust the MIC volume automatically? Try changing this setting to see if it makes a difference to the test call.
Please try to answer each question above individually so we get as complete a picture as possible of what is happening.