What is the best way to copy,delete and reinstall my operating system?

data, use install disks to erase and reformat (partition) the HD (Without knowing more about the crashing you may need a new HD if you're having problems).

Once that's done do:

1. all the OS updates,
2. copy back the data,
3. delete all the user/library/preferences, caches
4. run Applications->Utilities->Disk Utility->Disk First Aid:Repair Permissions before using (many problems can be caused by corrupt .plist and cache files.)

Remember to return and mark as accepted the answer that best solves your problem.

Good luck,

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