Lately in Sonar I have been using keyboard shortcuts a lot. But sometimes I accidentally hit a key combination that the Windows o/s responds to and does something unexpected. Today while working on a project I suddenly had no sound until I eventually noticed a mute symbol on the taskbar speaker icon. Yesterday, out of the blue, Windows started closing down and didn't save the project that I was in the middle of editing. On other occasions programs have unexpectedly launched. It's annoying.
 
Does anyone know a good way to disable Windows keyboard shortcuts?

I am not clear on what keyboard combinations are giving you trouble. There are several sources of fixed key actions that may be affecting a Windows system.
The first are Windows Logo key combinations (aka hotkeys) require the Windows Logo Key in combination with something else. These should not be happening unless the Windows key is pressed.
You might have inadvertently turned on Ease of Access (aka sticky keys) key responses.
The fact that you were able to mute your computer inadvertently suggests you may be dealing with a BIOS coded response that is common in laptops where one of the function keys controls the machine. Look for little icons on the function F1--F12 keys and check your computer manual. Typically these will be activated by another key (ctrl, Alt) in combination.
http://windows.microsoft.com/en-us/windows/keyboard-shortcuts#keyboard-shortcuts=windows-7
 

Thanks Slartabartfast, but it's not a laptop.  Ease of Access is all off.

It may or may not be significant that I didn't have the problem until I started using this keyboard:
http://www.jbhifi.com.au/...use-sku-66114-full.jpg
I never touch any of the side keys, but I could have easily caught my finger on the Windows key.

Kev999
Thanks Slartabartfast, but it's not a laptop.  Ease of Access is all off.

It may or may not be significant that I didn't have the problem until I started using this keyboard:
http://www.jbhifi.com.au/...use-sku-66114-full.jpg
I never touch any of the side keys, but I could have easily caught my finger on the Windows key.

Not a laptop, but the keyboard apparently has its own dedicated hotkeys that you might hit by accident. Exactly what these will do under Windows 7 is a question:
 
ftp://ftp.quatius.com.au/Manuals/cwk100.pdf
 

I never touch the hotkeys.  I know what they do but I don't really need them.  I believe that the problem is caused by me accidentally hitting certain key combinations.  What I am hoping to do, if possible, is disable some or all of the Windows keyboard shortcuts.  The PC is exclusively for DAW use and I only ever use keyboard shortcuts within Sonar.