Ok, so I turned on my daughter's MacBookPro circa 2011, a box popped up saying update available, install now and restart, which I did, it shut down but instead of restarting it got as far as the Apple icon and the daisy wheel continually turning.

Ok, so I turned on my daughter's MacBookPro circa 2011, a box popped up saying update available, install now and restart, which I did, it shut down but instead of restarting it got as far as the Apple icon and the daisy wheel continually turning beneath it. I've tried turning off and on a few times and also the Apple Hardware Test - i.e. holding down D key as soon as I turned on, but this did nothing except slightly delay the time it took for the Apple icon to appear, and the annoying daisy wheel. Someone suggested holding down Command and R while booting, but I am a little nervous in case this would delete any photos/music, etc., she has on there??

Any ideas please - I am not brilliant with tech but can follow clear instructions! I did manage to successfully remove a virus from a computer some years ago, on my own with help from t'internet - very satisfying!!