First try a hardware reset.
1. Unplug the USB power cable from the back of the Stream box.
2. Locate the Power button on the front (or side) of the box.
3. Press and hold that Power button.
4. While still holding the button, plug the USB power cable back in.
5. Continue holding the button for about 20–30 seconds. A "Welcome" screen will appear, then it should eventually switch to a black-and-white "System Recovery" or "Maintenance" menu.
6. Once you see that menu, you can let go.
7. Use the power button (short presses to navigate, long press to select) or the remote to choose "Hard Reset" or "Factory Reset."
Once done you'll need to sign in with your Virgin Media account (email + password) or complete the on-screen activation flow that links the box back to the account. Re-pairing the remote will have to be done too.
If this still doesn't work then there is a likely provisioning failure which only VM can resolve.