Comcast Constant Guard is a “free” security suite provided to Comcast XFINITY customers. It includes Norton by Symantec anti-virus, Identity Guard, Secure Backup & Share, and the Xfinity Toolbar. The protection is provided for iPhone/iPad, PC, and Mac. With a recent update, Comcast managed to break a number of customer’s computers with Blue Screen of Death errors after a driver conflict. The victims seem to mostly be HP laptops that have quick launch keys on the keyboard.
The relevant information in the error appears to be:
Technical Information: STOP: 0x0000003D
In typical “cable company”-level support, Comcast does not appear to provide any information on their site or with Constant Guard despite the significant portion of their customers potentially affected by this error. Fortunately, buried deep in a forum thread, a few solutions to move forward exist.
If you are receiving the Blue Screen of Death for the KeyCrypt64.Sys driver, you want to uninstall Comcast Constant Guard. Because of the error, it might take some effort to accomplish this.
Reboot your computer after the BSoD (Blue Screen of Death) and repeatedly hit the F8 key between the BIOS and the Windows splash screen. This should load the Windows startup options. If you can choose Last Known Good Configuration, select that option and let the system reboot. Once it reboots and you can log into the computer, head to the Control Panel and uninstall Comcast Constant Guard.
More complicated fix:
1. Boot your computer up using the Windows Install CD that will let you repair your installation.
2. Choose repair, select your hard drive instance, and finally select command prompt.
3. From the command prompt, run RENAME c:windowssystem32drivershpqkbfiltr.sys c:windowssystem32drivershpqkbfiltr.tmp
4. This disables your touchpad and keyboard so plug-in a USB keyboard and mouse.
5. Reboot the computer to windows normally.
6. As soon as you can get logged into Windows, head to the Control Panel, Programs and Features, and uninstall Comcast Constant Guard.
7. Reboot and repeat steps 1 and 2 and then use the command RENAME c:windowssystem32drivershpqkbfiltr.tmp c:windowssystem32drivershpqkbfiltr.sys
8. Reboot the computer and unplug the USB keyboard and mouse.
If you are having difficulty removing Comcast Constant Guard, you can try downloading and running its Clean Uninstaller.
Source: Comcast Help and Support Forums