I'll put a step-by-step review at the end
You may have deleted your sound card drivers (or one of the other audio devices) So this is what you do: hold the windows key(looks like a window

) and press the pause button. Thats just the shortcut for right clicking on my computer and going to properties

. Click the hardware tab and click the device manager button. Look for any question marks or exclamation points.
***If you see any ! or ? and still can't figure out what to do, list what devices have a ! or ?
Now if you see a ! or ? click the plus sign on that category. After that double click the device that has the ? or !. It will probably give you all the info. you need to find the drivers for that device. The brand for the audio device will probably stick out. Then you can either try going to the companies website directly, or search for it via a search engine. The companies website will probably have a section for software/drivers or drivers. Go into their driver section and check for the make of the audio device with the ? or !. If you find the correct driver download it. They may have you download a program that detects what driver you need, or maybe one that installs the driver automatically. Hopefully thats the case but if its not you want to go into the device manager like I stated before and click the + sign where you saw the ! or ?. Now double click the device again and click the driver tab. Then click update driver and browse to the location of the downloaded driver.
Now to review:
1) Windows Key + Pause
2) Hardware Tab
3) Device Manager Button
4) Look for ? or !
5) Click the + where you see the ? or !
6) Double click the device(s) that have the ? or ! to get more information about the maker of that device
7) Go to the maker's website and download the driver or program that installs the driver for you
----If the driver doesnt install automatically----
8) Repeat steps 1,2,3,4,5, and 6
9) Click the drivers tab
10) Click the update drivers button
11) Browse to the location of the downloaded driver
You may have to repeat this depending on how many devices have a ? or !
Hope this helps!!!
Shane McP