|That problem can be a pain - and on rare occasions can result in a loss of some data (but not always).|
What make and model computer are we talking about?
Can you boot it into safe-mode at least?
Prime consideration would be (for me at least) to recover/safeguard personal files and then set about resolving the actual problem as posted. Personal files can usually be copied ot external storage - typically dvd and/or an external hard drive; checking the copies are OK too on at least one other working system.
Even in safe-mode one can usually safeguard files. Another method is to boot the system with a Linux dvd and access/copy the files that way.
Ubuntu.com is where to find a free ISO file; which download and burn to a dvd. Boot with that dvd and then one can access the hard drive. The Linux OS will "not" write anything to the drive itself (unless you opt to install it there - which do not..); it merely installs itself into RAM only and the hard drive simply a resource for the RAM installed Linux OS.
message edited by trvlr