Interactive logon process initialisation has failed

I've just finished doing a boot time Avast scan on my nephew's laptop - but now after it finishes that and continues to load Windows, I get this message:



Sounds rather serious to me - can anyone help? I hope this doesn't involve having to send the machine away. I recently had to do a factory default reinstall as the system had stopped responding - no matter what I did (it started doing that after installing the Norton crap that came with it, so Norton's going nowhere near any system of mine in the future.

I'm going to try Windows' repair options, but I'm not too hopeful.

Edit:OK - after a couple of restarts (before trying Windows' repair options), Windows has loaded successfully. What could've caused this and what can I do to avoid it happening again?

No one at all? Has this been posted in the right place, if not could a mod please move it? Thanks!