2008 macbook pro

The link in step 6 of the article macjack referenced won't work on pre-2012 Macs; instead, you need to insert a compatible Mac OS X install DVD, restart with the C or Option key held down, use the Disk Utility to erase the internal drive, and then install a fresh OS.

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Follow the steps in this Apple Support Topic:

What to do before you sell or give away your Mac - Apple Support

Yes, thanks for the correction.