That sounds like a component failure which, regrettably, you won't beable to fix yourself.
Your first point of contact should be Hitachi's official service partner in the UK, Argos Direct, on 0345 604 0105.
If the set's fairly new (under 6 years old) hassle them for a repair.
Otherwise you'll either have to seek out an independent repair service or bite the bullet and look for a new TV.
Curry's/PC World won't be the cheapest for repairs but they do offer a 'no fix / no fee' service:
https://www.currys.co.uk/gbuk/tv-repairs-problems-371-commercial.html
Alternatively, of course, your telly might just have a bit of taste and be refusing to show the Eurovision Song Contest ;-)