Olympus e510 hot-shoe doesn't respond...

Sadly I think the problem is a design fault. Simply put the pins don't align accurately when you slide the flash unit on and lock it into position. There is slight misalignment, even though the locking pin has slipped into the slot.

I have had an absolute nightmare with the hot shoe on my E-510, and it took me ages to figure out what the problem was, having cleaned the contacts to within an inch of their lives!.

When you slide the flash on and lock it the pins don't connect accurately with the plates on the hot shoe plate. The only way I can get the **** thing to communicate with a flash unit or flash extension cable is to slide it on, partialy lock it and start gently wiggling the flash unit backwards and forwards until the flash icon on the menu screen lights up, then quickly finish the locking procedure.

Even that, though, doesn't guarantee consistent communication with the camera. Swinging the camera up and down between shots often jiggles the contacts out of alignment again and suddenly the flash won't fire again, neccesitating a repeat of the whole wiggle method. Often I have to turn camera and flash off and reboot everything again because once the camera loses communication it won't talk to the flash even when it's correctly realigned. It's either bad design or poor manufacture, but whatever it is it's a huge nuisance.

Have you tried cleaning the hot shoe contact? If the contact is dirty it may not communicate with the camera. The "contact" Its the metal "circle" in the middle of the hot shoe. Using a pencil eraser, rub the contact gently until you create eraser crumbs, then gently rub the "circle" with a soft cloth. See if this fixes it.