3 Times now, my new Z240 has become completely unresponsive! The symptom was that after pressing the power button, the button's light would come on, but nothing else would happen! My screens would never power up indicating that the video cards have initialized, I have no beeps from the onboard speaker, just nothing!
The first time this happened, I contacted HP Workstation support, and after running some diagnostics, they sent a tech out with a replacement motherboard. After that, everything worked just fine for about 1 1/2 months.
Last month, just before leaving on a trip, the system again became unresponsive - same symptoms! I didn't have time to contact support, so I just unplugged the system and left it for 4 days. When I returned, I plugged it back in, turned it on, and everything came back up as if nothing had happened.
Now, on Friday of last week, while trying to work out a video card issue (which I'm still dealing with 
), I updated the BIOS, and after it was installed, the system re-booted, and I did get the "Hp SureStart" message on screen, but it stayed on that screen for 4 hours! Eventually I gave up and did a hard power-down (held power button 4 seconds). After that, the system was again completely unresponsive. Remembering that the system came back last time after being unplugged, I pulled the plug and let it sit over the weekend.
Monday morning, I attached the plug again and tried to power up, but still nothing happened other than the power button lighting up.
I pulled out my support contact information (kept a copy on another computer so I could get to it again), and was ready to give Support a call, when I tried 1 last thing...I disconnected all USB and Ethernet cables and tried to boot again. Low and behold, the system came up again with no problems!
After much trial and error, I found that one of my 2 external USB drives (used for file history and a backup) was the culprit! Whenever that drive was connected, I'd either get nothing on-screen, or the boot would stop at the "Hp SureStart" message.
Once the system was up and running, I could then connect that drive and see all the files on it, but when I attempted a DiskCheck on it, the DiskCheck hung up, which forced me to reboot (after removing the USB drive).
Has anyone else experienced anything similar to this? The only thing I can think of is that this USB drive is placing too much drain on the power supply and preventing the boot. I would have thought that some kind of message (or beep pattern) would have happened to let me know that there was a problem - a completely unresponsive system doesn't tell me much!