I also had no sound on installing win7. Like above it was the REALTEK HD audio drivers.
I had this problem also.
REALTEK HD audio drivers
Your solution
I had this problem also.
REALTEK HD audio drivers
Your solution
Googling for something like 'no sound windows 7' won't help you out at all.
First thing to check is device manager and see if the sound card is installed correctly. If it has an exclamation mark by it or it's listed under 'other devices' as something like a 'multimedia audio controller' then you need to get the correct driver.