When I start my Windows 7, I get a notification

The system event notification service could not be started....

As a result, I dont have Aero, even though my Windows Experience Index is 3.2.
Aero used to work fine before today and I have not installed any new application. I have checked the event log and it reads:

The System Event Notification Service service terminated with the following error:
Overlapped I/O operation is in progress.

I am not sure what this means.

I have seen the services.msc and everything is fine there. Moreover the startup time has also extended and the Please wait stays for more than a minute. This is a sudden problem as everything used to work fine until today.

For Aero I have tried starting Desktop Window manager (as pointed out by the trouble shooter), but with avail. From what I could understand from the forums, the lack of Aero and increased start-up time comes from a single problem of the System Event Notification Service.

This is a personal Computer and I have no active directories installed.

3 Answers 3


I have this problem on my machine. It's been this way for a very long time. A temporary solution is to open services.msc, scroll down to the System Event Notification Service, and restart it. Then restart the computer; this usually fixes the problem for a little while. I'm still looking for a better solution.

If anyone has a fix for this problem, I'd love to know about it. My system is clear of malware, and a system restore is not an options since this problem has been in place for so long.

  • 1
    Tried all that bro!But to no avail.As far I could understand it is a hardware issue.Windows 7 waits a short period for your GPU to respond.If it doesn't then it switches to the no -Aero mode.There must be multiple reasons,but I figured out mine.! fine day my GPU started working perfectly and everything is fine now!
    – user38923
    Commented May 26, 2011 at 12:46

Check your system for malware first

How can I remove malicious spyware, malware, adware, viruses, trojans or rootkits from my PC?

Then if the system is clean, try a Windows restore point, choose a restore point before the strange behavior started. System restore may not solve the issue if the system is infected by malware.



TL;DR: Disabling the Windows Update service appeared to help in my case (CTRL+R, services.msc, right-click Windows Update, Properties, change "Startup type:" to Disabled, OK, Reboot).

It is unclear whether that actually helped but it coincided with my problem going away. The problem presenting as Win7 showing a bubble

"Windows could not connect to the System Event Notification Service service"

after login and looking Win98-like (grey taskbar etc.).

Like OP, I found the titular error message in the Event Viewer (CTRL+R, eventvwr.msc, Windows Logs, System), going back in time to find and check the most recent red exclamation mark. Then checking the immediate predecessors messages, I saw multiple services "entered the stopped state", last of them being SENS. Going back further, the first other kind of message was

"The Windows Update service entered the running state."

So, as initially described, I opened the the Services panel and disabled Windows Update. Not sure, you will want to keep it that way. After the next reboot the problem did not arise.

To be fair, the problem did not consistently appear beforehand but recent reboots only worked out at maybe a 20%-25% rate.

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