As I understand it, the global hotkey list is constructed into memory when Windows starts up so there isn't any one place you can go a look at them (e.g. they are not stored in the registry).
They appear to be defined (mainly?) in .lnk files so you would need to walk through all of the .lnk files on your system picking out the hotkeys.
As usual, someone has been here before and written a VBS program to list them all.
However, a quick look and attempt to run shows me that it is not very robust or complete. However, if you can get it to work, it may tell you what you need. Otherwise, you need to enhance it to search for .lnk files in other places. I'm also not quite convinced that .lnk files are the only way to register global hot keys.
However, I did stumble on the Hotkey Commander shareware, so this might do exactly what you want. Give it a try and add an update here so that we know if it works or not.
Oh, and this question is a partial duplicate of: How can I determine which process owns a hotkey in Windows?
UPDATE: I couldn't resist so I tried out Hotkey Explorer which is the free tool listed along side the shareware Commander tool. It does indeed seem to list all of the registered global hotkeys and their registering applications. It will be interesting to know if it is able to spot what is intercepting your keys.