f when you boot you don't have sound,there are 2 ways to fix it.
First(and not very effective) method:
Download drivers for your intergrated audio from the asus website.Install them,but when it prompts you to reboot,don't.You should have sound.(Keep in mind you mustn't have any open window at the time of the installation or you won't have sound).The bad thing with this method is that you have to do this every time you reboot.
Second(and permanent method)
Enter the BIOS and browse it until you find onboard devices.Open the submenu and change front panel type from hd audio to ac97.You should now,permanently,have sound.
Comment if it worked for you.
(I have posted this on win 7 drivers section too so that anyone can find it easily)
More about :ways fix sound problem asus p7p55d series win
Loading the sound driver from the online product page and enabling sound features in BIOS would not be instructions limited to the ASUS P7P55D. Besides loading the proper Windows 7 driver, Windows 7 has nothing to do with installing a sound driver and enabling sound in BIOS. Feels like I'm logged on to eHow..
I have Asus P7P55D. I bought it and installed it 8 months ago. I have had perfect audio since then. My front panel audio is set to HD Audio (default) because my PC case connector is HD audio (it also has AC'97 audio connector, which I did not connect), though I have never used front audio jacks. I have started with Via audio v.7300 drivers. Then v.7500 and now v.7900. I have no problems whatsoever. I guess I am lucky. Therefore, I did not have to apply your solutions.
I would like to note one thing, though. I could not play the sounds in Bluray movies 'Gladiator' and 'Good Luck Chuck' prior to v.7900. Many others played sound well with v.7500, such as bluray movies 'Casino Royale', 'Vacancy', 'Wanted', etc. Now they all can play well with v.7900.
Sorry for writing instructions that way,but I wanted even very unexperienced to be able to understand them.The point about the driver solution is that you mustn't reboot.As for the comment that this works for other motherboards too,I think I didn't have to say it,but anyway I have faced this problem with the p7p55d so that's the reason I say it's for the p7p55d series.
PS.Looking at my thread again it does look like ehow Next time I'll pay more attention.