External screen won't wake up after standby

I have exactly the same problem. Using a Macbook Pro 17" early 2011, with the same monitor, HP x2301. Driving me crazy. Happens in Lion, and in Windows 7 in my Bootcamp setup.

I'm having the same problem with a MBP 15" 2011. After unplugging the HP x2301 monitor it works again. I tried to connect it to both DVI and HDMI connector but it didn't solve the problem. Any clues?

I have the new 15" Retina MacBook Pro connected to a Thunderbolt display using one of the TB ports. Earlier today, I discovered that I could connect a second older 24" Dell Monitor (2405FPW) I've been using for years by using the Mini DisplayPort to DVI adapter I had on my old iMac, and plugging the Dell directly into the second Thunderbolt port on the MBP. All was well, until the displays went to sleep (I have my laptop configured to not sleep for 3 hours, but have the displays sleep after about 15 minutes). When I came back, moving the mouse and typing on the keyboard brought the Thunderbolt Display back to life, but the Dell monitor remained dark. Pressing buttons on the Dell had the message "In Power Save Mode - press key on the keyboard" appear. I tried turning the monitor off, back on, unplugging the DVI cable from the MBP, all sorts of things. It just would not wake up. When going to the System Preferences, the dell WAS recognized. As I plugged and unplugged the DVI cable from the second TB port, the "Arrangement" tab would appear and go away. So, it SEEMED like it was working.

Final solution for me: I selected "Sleep" from the Apple menu to actually put the entire machine to sleep. I then jiggled the mouse, and the machine woke up, along with BOTH monitors!

So, it appears that if just the monitors go to sleep, the "wake" signal is not making it to the Dell. If the ENTIRE MACHINE sleeps, they all wake together.

Hope that helps someone. I couldn't find an answer, so I found it trial-and-error.

It's very likely the monitor. I have a Samsung that does this if I use its DVI interface. If I use its VGA interface instead, the problem doesn't happen. But the DVI has better image quality.

The monitor tries to be intelligent about detecting which input interface to use. When my MacBook Pro goes to sleep, the monitor spends about 30 seconds switching between DVI and VGA looking for an input signal. After 30 seconds, it gives up and goes to sleep. In sleep mode, it stops checking both inputs. Even when the MBP wakes up and sends a valid DVI signal, the monitor ignores it because it's only watching for signal on its VGA interface. Turning the monitor off and on causes it to auto-sense again, it finds the DVI signal, and displays.

If you can force your monitor to only use the correct interface, rather than auto-sensing DVI or VGA, it might wake itself up properly.

In my case, using a Thunderbolt to HDMI adapter worked, when the DVI interface did not work. With the HDMI connection, the monitor now wakes up everytime, perfectly.

Use HDMI. It works when DVI does not, in my experience (HP monitor, 2012 Macbook Pro)