Hi Kate I use Nero.......It is an all singing dancing media player and burner.....it also has a neat cover designer that can print my own CDs and sleeves etc. For playing files I need and use several players depending on the application I need at the time.
Windows media player I find troublesome and it does not have the apps I need.

With regard to you missing certain components.....this can be fixed with a repair......This is straightforward and easy to do. The installation disc you have for 7 should replace/repair the missing bits. If you do not know how to do this then I suggest you ask someone to do it for you. You may be able to get this done under warranty or insurance.

With regard to you recording guitar/vocs I would suggest recording the vocals on a separate track from the guitar. Mic placement editing and adding FX is simpler this way and the end results would be so much better and sound more professional.
Record the guitar first and then playback through headphones whilst recording vocals on another track.
There are tutorials on Audacity that will help you with the tech issues.
This link might help you get started.
http://www.guidesandtutorials.com/audacity-tutorial.html

http://www.soundclick.com/bands/songInfo.cfm?bandID=687727&songID=5238055