Dear all, as you can read from the title I have had a nice surprise on my MBP. Normally I always put the machine to sleep and do not turn it off (even if before updating to 10.2 I had turned it off and on again with no problem). Yesterday I had to take the notebook away and so I turned it off. At the next turning on, the prohibitory sign appeared. Now, before you suggest something, let me list down what I have already done: - reset PRAM & VRAM - reset SMC - Safe Boot mode (Cmd+Shift+V) getting the message "Still waiting for root device" - I followed support.apple.com guidelines. - next, as soon as I went away to look for my 10.5 leopard disc, it completed the OS loading and the machine is working, slowly with let's say just fine. - called Apple Support this morning - out of warranty this machine is, of course - and they suggested Apple Hardware Test or reinstall the OS. - done AHT and got "no problem found" - rebooted, got the prohibitory sign, waited 2-3 mins and then the machine starts up. Now, as I have a whole lot of work going on I would like to know if this is a bad issue, if something can be done and if so, in what order. I thought about erasing disk (after backup ), installing leopard > snow leopard > mavericks and then stop there maybe as my machine is indeed supported by yosemite but now with the last update something seems to have gone wrong. Thanks for all your support B.