That depends on the problem. If you have a full hard drive, you might be able to get out of the situation slowly by saving currently open files out to a floppy, Zip, CD or other media. Then copy off material until you clear enough space to do more housecleaning.

If you have a bad sector issue, you might want to get something like SpinRite to recover the drive long enough to get the data off. SpinRite is inexpensive enough ($89 US at www.grc.com) that you can download and make a bootable CD quickly and get right to the problem. If the drive and data is salvagable, SpinRite will bring it up. Otherwise more forensics based tools may be required.