Hi, firstly the deadly 'sandbox' is seen by some as just theory and the sandbox is actually nothing more than a theory developed to explain what many different SEO experts have witnessed with their listings. What is known is that the effect of this exists. A way to determine if you have been sandboxed is to see if you rank (well) in the other major search engines, but do not show up at all in Google's rankings, you have probably been sandboxed. The sandbox is basically a filter and normally applies to sites ranking for competitive keywords, the only way to get out of the sandbox is to wait...
Just Search your domain keyword in google.If your site is www.mywebsite.com and you look for "my website" on google and you find nothing that means your are sanboxed... Once you start back link work by doing link building services and fresh content creation in few months you will notice you are now within page 1 or 2 for your domain keyword and that will mean that you are slowly getting out of the sandbox.