go here and select the exact c300, and your OS:http://h20000.www2.hp.com/bizsupport/TechSupport/ProductList.jsp?lang=en&cc=us&prodTypeId=321957&prodSeriesId=3213865&taskId=135
If U just installed, U should also download and install chipset driver, and video card driver also.
as for the sound, under audio, download and install.
Oh, you'll also need a good codec pack for your videos. Try K-lite codec pack, if U want your videos to run ok.