"No Audio Output Device is Installed"

Now like everyone with the same problem, I would love to curb this problem asap. The problem started about 5 weeks ago, I'm not sure what caused it but i have searched google and tried everything from windows update to drivers updates and chipset updates. No most of the fixes on the interwebnetz mention the device manager and disabling, then enabling the sound device.....but that's pretty hard to do if the device in question disappears from the list itself.

Ok so I'm running Windows 7 on one partition and Ubuntu 10.04 on another partition. Now I know both OS's had sound working, in fact it was working earlier today. However as soon as the problem appears in either OS, it effects both. One of the solutions mentioned whilst scouring the netz was to reinstall windows, but it's ridiculous to keep reinstalling windows in order to get the sound back. There are also times where I'm lucky and the sound will return for just that time I've turned it on, restart and it goes again.

The laptop is an Acer Aspire 7520, and I believe it has a realtek chipset.

I would really appreciate it if someone can point me to a solution. I can't afford a new laptop.

I was afraid it was going to be a hardware problem..well just to go over the other faults with this system. only 2 out of 4 usb ports work, the 3rd one is detected but anything plugged into it and the system says it tries to install drivers but fails. It thinks there are 5 USB ports. CD drive stopped working a while ago, not listed in the bios anymore

There are also times where I'm lucky and the sound will return for just that time I've turned it on, restart and it goes again.

Sorry, yeh it's when I've turned it off and then turned it on to use it the next day, sometimes it will have sound in a session, but as soon as its turned off and turned on another time it doesn't work again.

OK so i started it up this morning and it had sound, however when it went into hibernation due to low battery, upon resume I had no sound. I went into the device manager to see if it was still there and it was, so i decided to disable it but that just made the manager crash :/