翻译强力驱动Recently upgraded to Android Studio from 2.2.3 to 2., running on Win10
Emulator stopped working since then. Tried installing other images(25 rev 4)/upgrading for AVD but nothing seems to work. After running gradle and showing "waiting for target device to come online" in task bar nothing happens and program doesn't run.
Kindly help
Adding Screenshot:
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I was also having the same issue 2 days ago when i update my android studio, today I solve my issue when I was playing around with settings then I saw that in my SDK tools setting Android Emulator is uncheck so I simply checked that box and now emulator is working fine.
Try this steps may work for you also:
There are changes, though it's installed, you might need to update 
I already have Emulator installed. But still had the same problem this morning with Ubuntu 16.04 and Android Studio 2.3,Below is what I did and it worked.
Double Check to see if these are available:
sudo apt-get install lib64stdc++6:i386 sudo apt-get install mesa-utilsLocate the lib64 folder. On Ubuntu 64 bit, its located under ~/Android/Sdk/emulator/lib64.
In terminal, Navigate to the ~/Android/Sdk/emulator/lib64 folder ,then run the following commands:
move the libstdc++ file inside the folder libstdc++.bak and provide softlink
mv libstdc++/ libstdc++.bak ln -s /usr/lib64/libstdc++.so.6 libstdc++if you docker is running you should close it.
None of these solutions worked for me. After removing and installing the emulator from scratch several times, and also SDK Tools, I saw under developer options in the emulator that USB debugging was not active.
First delete your exiting emulator than recreate it. Now run again hope it will fix your error.
Try configuring different Android Emulator and using it while running. You current emulator may have some issues. It worked for me.
I had a similar problem when updated my android studio. Somehow it changed my SDK path. I just changed it to my updated SDK path and it worked.
Android Studio -> File -> Settings -> Appearance & Behaviour -> System Settings -> Android SDK
Here you will find Android SDK location just click on edit link in front of that and browse and select the Android SDK from the file browser. Select and click on Apply.
Select AVD manager and start Emulator. This solution worked for me.
I was experiencing the same issue where the emulator would start up but I would be left with a black screen and my app won't load up. Anyway, what I did was, I accessed the setting of the emulator. Make sure the "Save quick-boot state on exit for AVD Pixel_2_API_26" is set to "No". Note: My device is a Pixel 2, it could be different for other users. 
Restarting the computer solved it for me.
After lots of attempts, stopping device from AVD(exactly from AVD, not by cross button nor power off button on emulator) and starting build again helped me.
Upgrade your Display driver ... this worked for me!
maybe you do not have SDK of your simulator,please check File->Settings->Appearance&Behavior->SystemSetting->Android SDK
I had to turn off Parallels Desktop and it started working again without reboot.
For me what was happening was the Virtual device never booted.
What fixed this was:
cd ~/.android/avd// rm *.img Then I restarted the virtual device and it came on line.
If none of the previous answers solved your problem, I suggest you to check KVM errors. Even if you did not install KVM it's possible you to get KVM errors when you try to run x86 images. Open a terminal and type dmesg | grep kvm after starting emulator. This way you will be able to see if you get KVM errors.
On my Ubuntu 16.04 machine with Android Studio 2.3.3 installed on it, the problem was about KVM. Android Studio was trying to enable KVM for x86 images. When I try to start the emulator, dmesg showing errors "kvm: enabling virtualization failed." Although ARM images were working fine.
After installing KVM, I was able to run x86 images on emulator without errors.
If this is the problem you are encountering, you might want to checkout KVM installation page.
I tried doing a “Cold Boot Now” in the device, but got an error saying: AVD Pixel_API_24 is already running. If that is not the case, delete the files at /.android/avd/Pixel_API_24.avd/*.lock.
After deleting a .lock file in the suggested folder the “Cold Boot Now” worked and the device was back to normal.
I have the same issue with the new update about Quick boot.
Unfortunately I had to disable it to make the emulator working again.
Android Studio -> tools -> Android -> AVD Manager -> edit your emulator -> Show Advanced Settings -> select Cold boot
Setting the system variable ANDROID_SDK_ROOT to the path used by Android studio solved the issue for me:
In Android Studio fire up Tools>Android>SDK Manager, navigate to Appearance & behavior>System Settings>Android SDK
Copy the path from "Android SDK Location"
Add ANDROID_SDK_ROOT to your system variables and assign the path
Restart Android Studio