when i try to start my laptop i get a black screen saying that a change of hardware or software has caused my computer to shut down and gives me two options, run windows repair (recommended) or start windows normally - i tried starting normally several times, turned on and off, did ctrl+alt+del, unplugged all USB items, than i tried running windows repair, i ran the quick test and it said no errors were found, under tools i chose check and repair hard disk for C drive - it took an hour, said an error was found and repaired, did the same for E which took about 5 minutes and said no errors were found, than i tried to start again and i see the windows start up, than it just goes back to the same black screen with the same message, when i try windows repair it gives me a message saying my computer is running on a limited mode or something and cannot run the repair, when i "x" out of the repair screen or push "esc" it tells me that something is wrong with the OS C drive - but i don't want to run the C drive repair because i have years worth of work on the computer that is not saved anywhere else and cannot loose my files - please help, i know nothing about computers and how to fix this and am freaking out, plus i have a huge meeting on tuesday for which i NEED my computer! 
