Q: My iMac will not complete booting up

Unfortunately, here in Spain, my nearest Apple Store is about 2.5 hours away. Bit of a trek, if I have to leave it for repairs.

If I try the command+option+r, where will I find myself if it works. Do I have options to select? Am I up and running? will I have to re-install OS X, and why do I do that? Just trying to understand what and why am am doing things. Also, if I have all my photos and documents backed up to the cloud, would I lose anything by trying to repair?

thanks for your patience and help.

HI, sorry I suddenly disappeared off the site. Been on holiday. Got back to the problem yesterday. Followed your instructions. Problem on Hard disk could not be repaired, so had to erase disk, and reinstall OS X. It has downloaded OS X Mountain Lion. Not sure if that was what I was on before! Anyway, system appears to be operating OK, so far. Have run an update on Apps. Just downloading apps now, on my fairly slow wifi! Following this, I need to try to see if I have stuff saved on iCloud I can download. Any advice would be very welcome. I can't seem to find Photos App. Do I have to download from App Store?

thank you so much for your help. Once I have everything up and running, I think I will go and buy an external hard disk, and back up to that!

IMac 27 inch Late 2012. 2.9 Ghz Intel Core 15. 8GB 1600 MHz DDR3 Should I be running a Software Update?

On About This Mac, it says Software OS X 10.8.5 ( 12F2560). When I click "Software Update" it checks then comes back No Updates Available. Does that mean this is as good as it gets?

ON the App Store I have option of free upgrade to El Capitan. Is that what I want or not?