Repair start up disk?

I wanted to run OnyX but it said something that I had to repair the start up disk? What would cause this? Should I do it? (it says something about using a Mac OX cd/dvd). Will I lose all my stuff on my computer?

I'm so bad with computers

Help please!

I cannot answer for your computer but I just downloaded the same program a few hours ago and got the same message. I followed the instructions and fixed the problem and have had no problems.

Sunshine use your install DVD that Tiger came with, insert DVD and reboot holding down 'C'. When it boots go to Utilities.Disk Utility and run Repair Disc. It will give a report and hopefully say all is well and repaired.

You will not lose anything UNLESS you select 'Erase and Install' and not Utilities.

I just had to go through it for the first time a few hours ago.
Worked fine, now everything seems to be ok.