When I disable Avast it shuts off my computer

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I want to disable Avast when I don't use the internet.  I like to use excel and access and my computer runs much smoother when avast is disabled. 

I tried to disable Avast the last two times and it just shuts down my computer.  Any ideas of why it is doing this.

Thanks

[Pondus]

  I like to use excel and access and my computer runs much smoother when avast is disabled. 

Do you have any other security programs installed?

I tried to disable Avast the last two times and it just shuts down my computer.

How did you disable avast?

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Nope, I don't have any thing other than Avast!

And I disable it by clicking on the avast! icon in the right lower corner.  I right click on it and go to Avast! shields control> Disable until computer is restarted

It works sometimes but other times I disable the program and my computer goes to a blue screen and says something about garbage dumping or something like that.  It then restarts and then asks me if I want to start windows on safe mode or just regular windows.