Although it's quite possible that it 'just happened' (like hardware failures do), I'd start with looking for Windows 8.1 drivers on the Lenovo site.
isn't it a strange time to update from 8.0 to 8.1 while the whole world upgrades from 8.1 to 10?
Kees
updated from win 8.0 to win 8.1 on Lenovo g500. wireless connection does not work.

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