How do I delete everything off my computer?

If the keyboard doesn't work, then why do you need to erase the hard drive? Get the keyboard fixed first.

Hard to do without a keyboard.

What to do before selling or giving away your Mac - Apple Support

If your computer came originally with Snow Leopard or earlier, then instead of Step 6 in the above do the following:

Clean Install of Snow Leopard

1. Boot the computer using the Snow Leopard Installer Disc or the Disc 1 that came

with your computer. Insert the disc into the optical drive and restart the computer.

After the chime press and hold down the "C" key. Release the key when you see

a small spinning gear appear below the dark gray Apple logo.

2. After the installer loads select your language and click on the Continue

button. When the menu bar appears select Disk Utility from the Utilities menu.

After DU loads select the hard drive entry from the left side list (mfgr.'s ID and drive

size.) Click on the Partition tab in the DU main window. Set the number of

partitions to one (1) from the Partitions drop down menu, click on Options button

and select GUID, click on OK, then set the format type to MacOS Extended

(Journaled, if supported), then click on the Apply button.

3. When the formatting has completed quit DU and return to the installer. Proceed

with the OS X installation and follow the directions included with the installer.

4. When the installation has completed your computer will Restart into the Setup

Assistant. After you finish Setup Assistant will complete the installation after which

you will be running a fresh install of OS X. You can now begin the update process

by opening Software Update and installing all recommended updates to bring your

installation current.

5. If you are planning to sell or give your computer away, then do the following:

After you reformat your hard drive and reinstall OS X, the computer restarts to a

Welcome screen and asks you to choose a country or region. If you want to leave

the Mac in an out-of-box state, don't continue with the setup of your system. Instead,

press Command-Q to shut down the Mac. When the new owner turns on the Mac,

the Setup Assistant will guide them through the setup process.

Download and install Mac OS X 10.6.8 Update Combo v1.1.

You could get and use an iFixit.com repair guide (for takeapart) to remove the internal

storage drive (hard drive, ssd, etc) so you could access it by another computer's disk

utility, a simple secure erase or complete reformat may do it. This would wipe the

recovery partition on the hard drive, so this is not recommended unless you were to

go online and restore the system from Apple servers.

• iFixit repair/takeapart guides: https://www.ifixit.com/Device/Mac

A bluetooth keyboard may not work under certain circumstances, a USB keyboard may

do OK, even a Windows PC keyboard if you know which keys to try & use.

• Using PC keyboard with a Macintosh: https://support.microsoft.com/en-us/kb/970299

If the computer was damaged, then you could physically destroy the hard disk drive so

it could not be read. A big hammer? Maybe. Or, friend with an oxy-acetylene torch, etc.

And if the unit requires a repair, then it won't be worth anywhere near retail. A shop that

repairs those, may charge you less a fee to remove the hard drive, if they want to buy it.

Which computer model sales build year Mac are you having this issue with?

Also, if your computer did not ship with Yosemite, and had a previous system

on board, then you could attempt to start in Recovery and re-install the original

OS X. If the computer is old enough to have an install-restore DVD, then that

is the correct tool to try & use to erase/install a new non-personalized system.

A trip to an Apple Store with Genius bar, with an appointment, may be of help to get the

unit to work, or see why it won't. If there is a warranty still, then it may be sent to repair.

In any event...

Good luck & happy computing! 🙂