Q: mac mini ppc

- What model Mac do you have?

You subject line contains PPC, However, your profile says Mac OX 10.6. A PPC Mac can go beyond 10.5.8.

- WHat happens when you do boot? What shows on the screen? Does Power light come one? Do you hear the startup chime?

- Try resetting the SMC and NVRAM/PRAM

Intel-based Macs: Resetting the System Management Controller (SMC)

https://support.apple.com/en-us/HT201295

About NVRAM and PRAM

https://support.apple.com/en-us/HT204063

- Try starting in Safe Mode

OS X: What is Safe Boot, Safe Mode?

https://support.apple.com/en-us/HT201262

- Boot fromm install CD/DVD and repair the startup disk

- If it is repairable reinstall the OSX

How to reinstall OS X on your Mac - Apple Support

https://support.apple.com/en-us/HT204904

You will have to do it from install disk since likley your Mac does not have Recovery partition

- If you do not have a backup use disk utility to restore the internal disk to an external disk so you can try to recover data.

Then format the startup disk and do a fresh install of OSX