Quote:

but no message on display, just the led blinking (???)


That is nearly always due to a blown fuse (or two) on the mainboard.
There are three tiny surface-mount fuses around where the display cable
connects to the mainboard. These get blown when people reconnect
the display cable in the wrong position (like I did, once), but sometimes
also just blow on their own.

Not hard to replace if you can solder electronics, or if you know somebody
(at work?) who can do it. RobS, Stu and myself all have the fuses.

Cheers