Why multiple spucworkerprocessproxy.exe processes shows up when I even have one sandboxed solution deployed?
Sharepoint 2010 User Code Host Service kills all spucworkerprocessproxy processes, when stopped.
Go to Run-> Services.msc -> Please check if the "SharePoint 2010 User Code Host" service is running. If running then please reset it and try to create a simple Event receiver/Web part to confirm whether Sandbox Hosting service is up and functional.
Or in other words develop a "Hello World" web part and deploying it as a Sandboxed Solution. As soon as I try to add the web part to a page and verify if service is running fine.