If you have the original discs that it came with, you can boot from those disk and reinstall it back to factory default.

If however, you don't have it.  Deauthorized your computer from itunes and appstore and delete your files from it and see if you can do a secure erase on the free space.

Also, uninistall any apps you've added.

How do you do a "secure erase"?

Bimmer - not meaning to jump your posts.

Sarah,

Depending on what OS we're talking about when you boot into the installer disk, you can select "utilities" in the drop down menu. From there select "disk utility" and you'll have the options of different security options for erasing the drive.

Be aware that a high security erase can/used to mean multiple passes and, in the care of a large drive , mean many hours. 19 in one that I did just for grins.

>recycling a computer<

Ohh if it's in fair shape I repair/set them up and donate them into the inner city. Currently Portland, before Chicago. (Check out my history.) Always hate to see a good Mac in the recycle bin.

•How to prepare your Mac for sale or donation

general steps to deauthorize iTunes, & misc  + secure erase, install original OS X:

•How to reinstall Mac OS X from scratch

restoring your machine to an “out-of-the-box” state

The above, from TheSafeMac site.

Below are from Apple Support site pages:

•What to do before selling or giving away your Mac

•Deauthorize your computer using iTunes

To prepare a working computer for re-use enhances its value and does not add to the

wasteful stream of electronic junk; if the computer has a defect & cannot be restored

to its original software before giving away or selling, you could use an iFixit guide or

ask someone to extract the hard disk drive from the computer prior to 'disposal' and

you may be able to get a USB Universal Adapter Kit to connect the bare hard drive to

a computer via USB port, to see if you can save any content you want, & use another

Mac OS X disk utility to erase the drive.

If the older computer has FireWire ports, it may be possible to totally erase and then

reformat the internal hard disk drive of that unwanted machine, by use of FW cable

and if the old Mac can be started in Target Disk Mode, it will appear to the healthy

computer as an external hard disk drive, with its icon on the desktop. This would allow

you to use Disk Utility, in the healthy Mac, to erase (single-pass secure erase) a HDD

and check into reformat options similar to that of the computer; the HDD may be OK.

{Later machines with Thunderbolt data ports may be use a FW to TB adapter.}

IF FW Target Disk Mode can work, the details in this article may help use it:

•How to use and troubleshoot FireWire target disk mode

The iFixit guides can be helpful for repair or take-apart. Either requires skill, ability, etc

and a good degree of attention to detail, drawing yourself a re-assembly map, & clean

work space without interruption or distraction. Additional damages may result from use.

And there may be helpful take-apart video or other guides on web sites belonging to

resellers of upgrade or replacement parts, hard drives, etc. re: OWC macsales.

•Mac Repair Guides - iFixit:

https://www.ifixit.com/Device/Mac

Good luck & happy computing!