Ordinarily a 'no satellite signal' message would indicate a fault with your dish setup or the connections to your Sky box. You could check that the cables are still securely fitted to dish inputs 1 and 2 after switching off at the plug.
However, given the history you describe I'm wondering if the box itself has become faulty.
If you report it to Sky their response will be to upgrade to Sky Q - they won't send an engineer for Sky+ faults unless you have Sky Protect. You coud engage a local satellite installer to come and take a look or alternatively purchase a replacement Sky+HD box from ebay etc. (£30 max) but if it's a dish fault it obviously won't help.
