Hi Smerf...
Sorry to hear about your A4000 but it will most likely be something that can easily be fixed...
In 25 years of using the Amiga I've never had one develop the slightest fault let alone break altogether. My main A1200 in the tower has been running 24/7 since 1996 and still works fine even to this day along with my Microvitic MultiSync monitor why hasn't even been switched off in over 6 years...
I reckon myself the stress put on most systems that breaks them is the constant switching on and off of them (the initial surge each time on power up shortens the life of the components) the only time my main miggy goes off and my monitor is if we have a power cut...
Also those that leave them in cupboards, lofts, garages etc... and only power them up once in a blue moon are just asking for trouble, as the initial surge/shock on power up to things that have been left so long can easily blow stuff in the blink of an eye...
In fact the only repair I've had to do was on an A1200 I bought from ebay recently that had a gfx flicker problem, the owner said it had been up in his loft for at least 10 years but it was easily fixed with a new 1uf capacitor...
Of all the electronic devices I use the Amiga has to be the hardiest piece of equipment I've ever came across...
Cheers
Franko
