Samsung Galaxy S2(Format or restore factory setting through pc?) I accidentally sat on my Samsung Galaxy S2 and it has resulted in screen crack. I am planning of repairing it instead of buying a new one.

The phone with the cracked screen works (except the screen) and contains personal and sensitive data.

I do not want to expose it in any way while I give it for repair.  It would be nice if I can factory reset or wipe the phone before I give it to service.
A hard reset restores the original factory settings and erases content, including downloaded ringtones, images, programs, and contacts stored in the internal memory. This feature allows for resetting of sound profiles, display settings, and phone or memory card settings.

To perform a hard reset using the hardware keys, follow these steps:


Turn off the device. 
Press and hold both Volume Up and Volume Down keys at the same time.
Press the Power key only until the phone vibrates once, then release only the Power key.
Continue to hold the Volume up and Volume Down keys until the Android System Recovery screen appears. 
Press the Volume Down key to highlight Wipe Factory Data.
Press the Home key to select.
Press the Volume Down key to highlight Yes - Delete all user data.
Press the Home key to select. Press the Home key to reboot.


But as you said, your screen is broken. Check the screenshots and see how many times you want to use down and up volume key, so that the according to number position you can do it.