NO SOUND AT ALL NO SPEAKER SHOWING AT BOTTOM

Hello,
I've installed software to a USB cable for my cellphone. I also purchased a printer. I already had a printer hooked up to my system, but I took it off when I got the new one. The new one wasn't COMPATIBLE with my computer. I have Wndows XP. I put the old printer back onto my system and returned the new one that wasn't compatible to the store, but every since I did that with the printers... I have been unable to HEAR anything.... my pc will not play audio cds at all either when it was before. The speaker isn't even displayed at the bottom right corner of the screen either. I have an AOL Optimized (brain)... so if someone has the same one could you let me know if I have my audio cable in the correct place... or is there some way that I can fix this because I keep getting the msg: NO AUDIO DEVICES INSTALLED. please help me asap or let me know if there is software that I can purchase or obtain for free that will allow me to HEAR again?? thanks