if i reinstrall mac os (snow lepord) will i loose my files,i have no backup and i mac wont start , safe mode never gets past spinning loading icon and i left it all night

Normally a reinstall won't destroy any info that's not already messed up, BUT your in a real fix. 😟

You can't or do not want to try any install on an unrepaired disk.

I'd get an external drive, install OSX to that & see if we can recover any info from the internal drive.

I fully agree with BDAqua.

Don't do anything with this Mac until you have an external disk which you can boot your Mac from.

Not all USB disks are easy to boot from - FireWire is better

When you have a suitable empty external disk I advise:

1. Put install DVD into damaged Mac
2. partitioning external disk into 2 volumes
3. install OS onto one volume of external disk
4. Don't import anything during install process - it may reintroduce historic problems
5. Boot external disk
6. Use finder to copy critical data from Mac to volume of external disk with OS
7. Use Carbon Copy Cloner to clone the whole Mac hard disk to the other external volume
8. Boot into installer DVD and erase Mac's internal disk
9. Partition internal disk into 2 volumes and install OSs as required

OK, good luck, please keep us posted. 🙂