Sounds similar to mine; the issue was related to a faulty PSU with my 840AV. With the stock PSU it wouldn't chime, ended up switching it with that from an 8100 which looked much beefier and better quality.

It's still not 100% though, only chiming and booting first go, but it will not restart. Works fine but I have to leave it be for an hour or so before I can boot it reliably again

JB