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Something is interfering the bluetooth trackpad or trackpad itself has problem. That is why it is stuck at top left. Do you have any wireless mouse or bluetooth mouse there ? If so, switch it off or remove their battery. Check if you are able to use trackpad now.
If not, then turn off the Mac. Then remove the battery from trackpad. Wait 2 minutes. Put it back. Boot into OS X Utilities screen and does the trackpad works now ?
If not, then remove the battery of trackpad. Connect a USB mouse and use it to reinstall the OS X. Or after selecting Reinstall OS X, press the tab button on the keyboard and use it to move selection to the Continue button. Then press Space to click Continue. Use tab key on keyboard to switch between buttons on screen and press Space to confirm.
Please let me know if that didn't work, so we can continue troubleshooting.