Look at the boot CD of SystemRescueCd.
You can find on the SystemRescueCd website documentation in the form of both a Quick start and a Manual.
Use SystemRescueCd to boot and copy your files to an external disk, verify that you have everything saved in at least two copies, before wiping out your disk and restarting from scratch and installing anew Scientific Linux
(and in that case, do not go this time for dual-boot).
You may alternatively use a boot CD of Ubuntu or whatever other flavor of Linux that
you feel comfortable with.
If you can take out your hard disk and use it in another computer, you could backup
your files without a boot CD.
Sorry for this brutal method, but I don't think that it's possible for me or
somebody else here to fix your disk without hands-on on your computer.
If I tried doing remote-control of your efforts through this forum,
I could do more harm than good.
I also cannot go to more details than that, because tutorials are not allowed by the rules of this forum, and probably the available documentation may be better than anything I could do.
If you don't feel comfortable with this, don't take chances with your data
and get help from a more experienced person.
Next time, ensure that you always have external backups of your data.