Hi. If you can hear them, then you have no problem with the driver. You must play around with the Audio Properties.
1) Right-click the Sound Icon on the taskbar. 2) Choose Recording Devices. 3) Make sure you configured properly which device is the Default one, and check for volumes on it´s microphone and disable enhancements.
But since you mentioned to download the audio driver, looks like someone´s been playing with it. So the best way to get it is going to the manufacturer´s site: www.acer.com , choose location, choose drivers & downloads, follow instructions. MAKE SURE you select the correct operating system (Right Click My Computer, Properties...)