Audio Windows cannot verify the digital signature for the driver

Hello,
I installed window 7 in my computer and lost the audio output device. I have tried to resolve the problem by following the procedures you helped my fellows previously I only ending up getting the messege "Windows cannot verify the digital signature for the drivers required for this device. A recent hardware or software change might have installed a file that is signed incorrectly or damaged, or that might be malicious software from an unknown source. (Code 52)" for device status.

Help please.