|Avoid disabling anything which is Microsoft. Most are marked (in pink I think) but not necessarily all of them, so you might need to Google to determine whether some are MS or not.|
The following are definitely not MS so you could try disabling these for starters:
Although context menu's are a good place to start, if necessary I would extend this to disabling other ShellExtensions. I assume you have the filter set to Context Menus, but you can "select all" if it proves necessary. This will of-course result in a much longer list.
Your problem might not turn out to be a Shell Extension is but it is as well to eliminate this possibility.
some other bloke...