Windows 7 - Startup Sound?

Try this:
Sounds - Change

If it will not help, post back.
We will try Taking ownership of the file (but It's not much recommended, so try normal way first)

I found this try it.
How to change Windows 7 startup sound

Did you try it in safemode? You might have to take total control of all system files to pull that one off.

How to Delete a System File in Windows 7 or Vista :: the How-To Geek

Or maybe you can try the officially unsupported TechNet way of changing the default start up sound.

Startup sound

Yes, I tried it in Safe Mode. Still no luck. But I didn't use the DOS instructions.

Your technet link does not work - can you check it for me?

I do not think you can change the Sound from Control Panel, but there are ways one can use [Use it at your own risk]

1) For best results, boot out of Window 7 and into an alternative OS, such as XP. (This is assuming you dual boot.)

2) Locate the file "imageres.dll" in Vista's System32 folder. For instance, C:\Windows\System32\imageres.dll. Copy that file into a different location, i.e. your desktop.

3) Download ResHacker .

4) Open ResHacker. Open the imageres.dll file in ResHacker.

5) Find the folder that reads "WAVE" and expand everything below that.

6) Right click 1033 (this could have a different name depending on your locale), and click Replace Resource. Click "Open file with new resource", and find the wave file you want to replace it with. Once you're done, in Resource Type, type "WAVE", in Resource Name type "5051", and under Resource Language type "1033" (or whatever number you have). Once done, click Replace.

7) Click File, then click Save. Now you can copy this file to Vista's System32 folder.

Keep the imageres_original.dll file ResHack left behind in case you want to revert back to the original sound.

8) You might have some Permission issues while replacing the old file, if you have linux live cd handy, copy the new dll to a thumb drive & boot off from it and replace the file.