Switch your Sky box off at the plug and check the dish connections at the back of the box. Leave the box switched off for 4 minutes. If the dish connections are secure, and the problem remains after switching on again, it looks like a fault with your dish setup.
Unfortunately Sky no longer provide engineer support for Sky+ equipment unless you have Sky Protect so you'll need to engage a local satellite engineer to take a look for you. If you're connected to a communal dish, speak to your .landlord or their managing agent.
