Check the x-mitter batteries. (is the x-mitter light glowing, is the x-mitter antenna up etc. I find that my VS tanks are very sensitive to weak x-mitter signals)

Switch it off and on again underneath. And check that the reciever crystal is inserted properly.

Open up the hull and look to see if there are any obviously loose solder connections. (the warranty will probably not be worth the shipping back and forth, but check this out first)

You can also buy a VS tank repair manual from amazon.com.<br type="_moz" />