Carol's Macbook Pro prompted a bag of complaints from her recently. It finally quit abruptly while updating the FireFox browser. I spent a few days attempting to download a new OS X for her. No luck. The Macintosh HD kept showing as all okay in Disk Utility but refused to mount. I could boot from the backup drive I made for my iMac (very slow) but the internal Macintosh HD still refused to mount and be visible!
On the other hand my old 24 inch iMac made a year or two earlier did let me purge it and reformat and reinstall the OS X Mavericks. It worked like a charm and Carol spent Sunday afternoon cleaning the keyboard, magic pad, and screen with alcohol and invisiglass using a pin and a dental scraper on the keys as they had a decade plus of grime and dirt on them.