After instalation of windows 7 - says "no audio output device instaled
This will be because you havent installed your device drivers.
if you do a start search for Device Manager and open it up you may see a lot of things with a yellow triange with an exclamation mark in it. This means the software drivers are not installed.
Firstly, try running Windows Updates.
Failing that you will need to either:-
- If the PC is branded you will have to go to the manufacturer website, enter your model and get the drivers.
- If the PC is custom build you will need to get the make/model of the MOTHERBOARD (you can use speccy to get you that). Go to the manufacturer website and get drivers.