Check the capacitors on the power supply board. Even if they are not visibly bulging it's worth swapping them to see (as capacitors are cheap).
Thanks for the hint, do you know how to get the case open it looks like it needs a key?
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Don't know that model. Generally you have to take the stand off. If no screws -- look for small gaps in the screen surround edge which correspond to clips inside that release when pressed in with a small screwdriver.
Incidentally, though I'm not sure what the legal position is with a company purchase, the warranty expiry probably isn't an issue. Law in most jurisdictions assumes a consumer durable like this should last a reasonable time -- 5 years would seem about right given my experience of LCD screens. Must be worth talking to vendor -- if only in order to retain goodwill they should be able to do something.