snow leopard hung up on launch

my imac is about 4 years old, a few months ago I upgraded to Snow Leopard. Ever since it will freeze sporadically and be slow. Anyway last night it froze and a restart didn't help. Tried the safe boot, no luck, and then the command-s fsck-fy thing ... no results. All Im getting is the grey screen, apple and spinning wheel.

I have six weeks of a project 99.9 per cent done and deadline yesterday. I need to save those files. Should I reinstall Snow Leopard, or the older OS, and if so how do I, and will it cause me to lose my files?

ANY help would be much appreciated.

With an iMac that is four years old, the problem could well be a bad hard drive. Which it does sound like....

Backups, have you been making them? If you have no backup, you may well lose your project if the files on that drive can not be rescued. Reinstalling the operating system, even if it does work, may result in overwriting the data that's already on the drive.

I would try using Disk Warrior to see if it can rescue your files from the drive. Here is the LINK to the download. It's $99, so you might want to try the trial version first.