When installing an NVidia driver, it is highly recommended to exit Boinc and stop crunching tasks.
Performing a clean installation is also highly recommended (done through the advanced option).
Once you have installed the driver, restart the computer.

I recommend you install the driver when logged on as an administrator, and to only install WHQL drivers.
Using Beta drivers is not recommended for most crunchers.

For GK110 cards (GTX780, GTX780Ti, Titan and GTX780Ti Black Ed.) use a driver equal to or later than 331.40.

For an explanation as to why you need to exit Boinc see this post.
Post any comments in the same thread.
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FAQ's

HOW TO:
- Opt out of Beta Tests
- Ask for Help