I have no security software installed, nor has any been installed for a long time. Just MSE.
Then MSE crashing Windows is quite unusual.
Does this mean that you've had MSE running successfully for a very long time and this problem has recently begun? When did the problem start? And MSE needs to be open to the main interface to cause the crash or does it crash when it loads in the system
Any other recent changes on the system?
Unfortunately, if you are in North America, there is no longer any assisted support from Microsoft, but you could pursue this as a potential infection.
This web site - http://www.bleepingcomputer.com - contains details for many of the common infections, often immediately after they began to appear in the wild, and instructions are provided for
how to remove the infections using their malware removal guides. They also have forums where you can seek help from people who specialize in malware removal.
This may also be helpful - How to get rid of malware: