I'm running a high-ish spec Compaq desktop with Window 7 installed and a sound card integral to the motherboard.
All sound worked perfectly until I installed Skype. Now I can't get any sound out of my speakers.
I have uninstalled and reinstalled the driver for the Realtek HD Audio Device but to no avail. No flags in the device manager to give a clue. Visually all seems normal. The speakers work on another PC.
Try this, right click the icon in notification area, select playback devices and make sure Speakers is selected as the default device. Under the communications tab check the button is dotted for 'do nothing' or ' reduce the volume of other sounds by 80%'. Also in the box, under playback tab, you can configure and test you speakers. If you have Realtek HD Audio Manager installed then also check the settings there.